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{{short description|Public transport mode}}
'''Personal rapid transit''' ('''PRT''') is a category of proposed ] modes designed to offer automated on-demand non-stop transportation between any two points on a network of specially built guideways. The concept dates back to the mid 1960s. Although elements of PRT design have influenced the design of some existing ] systems, as of ] no PRT project has yet progressed beyond the prototype stage.
{{Update|date=February 2024|reason=There are many references throughout to what 'will', 'may', or 'should' happen when implemented; there are several PRT systems operational}}
] vehicle on a test track at ], ]]]
]'s ], ]]]
{{Automated track-bound traffic}}
'''Personal rapid transit''' ('''PRT'''), also referred to as '''podcars''' or '''guided/railed taxis''', is a ] mode featuring a network of specially built guideways on which ride small automated vehicles that carry few (generally less than 6) passengers per vehicle. PRT is a type of ] (AGT), a class of system which also includes larger vehicles all the way to small subway systems.<ref>{{cite book |last1=McDonald |first1=Shannon S. |title=Encyclopedia of Sustainability Science and Technology |date=2012 |publisher=Springer |isbn=978-1-4419-0851-3 |pages=7777–7797 |url=https://link.springer.com/referenceworkentry/10.1007/978-1-4419-0851-3_671 |language=en |chapter=Personal Rapid Transitpersonal rapid transit (PRT) systemand Its Developmentpersonal rapid transit (PRT) systemdevelopment}}</ref> In terms of routing, it tends towards ] systems.


PRT vehicles are sized for individual or small group travel, typically carrying no more than three to six ].<ref>{{cite journal|last=Gilbert|first=Richard|author2=Perl, Anthony|title=Grid-connected vehicles as the core of future land-based transport systems|journal=Energy Policy|volume=35|issue=5|pages=3053–3060|doi=10.1016/j.enpol.2006.11.002|year=2007|citeseerx=10.1.1.661.3769}}</ref> Guideways are arranged in a network topology, with all stations located on ], and with frequent merge/diverge points. This allows for nonstop, point-to-point travel, bypassing all intermediate stations. The point-to-point service has been compared to a ] or a horizontal lift (elevator).
Although the design concepts and engineering challenges of PRT are well understood, questions remain about its actual production and operation costs, its safety, aesthetics, and acceptance in a public installation. Past failures have been caused by: lack of financing; concerns about cost overruns; conflicts with regulatory agencies; political interference in the design requirements; and flaws in design and/or engineering. There is also opposition from advocates of other, more proven transport modes. Some fully-automated rapid transit systems do now exist, for example the ].


Numerous PRT systems have been proposed but most have not been implemented. {{Asof|November 2016}}, only a handful of PRT systems are operational: ] (the oldest and most extensive), in ], has been in continuous operation since 1975. Since 2010 a 10-vehicle 2getthere system has operated at ], UAE, and since 2011 a 21-vehicle ] system has run at ]. A 40-vehicle Vectus system with in-line stations officially opened in ],<ref>{{cite news|title=PRT System to Open for Suncheon Bay Garden Expo|url=http://kojects.com/2013/02/13/prt-system-to-open-in-april-for-suncheon-bay-garden-expo/#more-1411}}</ref> South Korea, in April 2014.<ref>{{cite web|title=Suncheon Bay Project, South Korea|url=http://www.vectusprt.com/EN/first-project/|access-date=2013-06-22|archive-date=2013-06-11|archive-url=https://web.archive.org/web/20130611220553/http://www.vectusprt.com/EN/first-project|url-status=dead}}</ref><ref>Masdar City and Suncheon have only two passenger stations while at Heathrow the two stations at the carpark are very close to one another. Masdar also has three freight stations.</ref> A PRT system connecting the terminals and parking has been built at the new ], which opened in 2021.<ref name="jqknews.com">{{cite web |title=Just now! Its in Beijing! Chengdu Tianfu International Airports first public appearance |url=https://www.jqknews.com/news/206726-Just_now!_Its_in_Beijing!_Chengdu_Tianfu_International_Airports_first_public_appearance.html |access-date=10 June 2021 |archive-date=10 June 2021 |archive-url=https://web.archive.org/web/20210610080711/https://www.jqknews.com/news/206726-Just_now!_Its_in_Beijing!_Chengdu_Tianfu_International_Airports_first_public_appearance.html |url-status=dead }}</ref><ref>{{Cite web |title=New airport opens to flights in China's Chengdu |url=https://www.shine.cn/news/nation/2106271175/ |access-date=2023-02-12 |website=SHINE |language=en}}</ref>
Because there has never been a real world installation, PRT is a controversial concept. PRT proponents claim that it could provide service that matches the speed and convenience of ] and ], surpasses the social and environmental benefits of conventional mass transit, and costs less than either. This has yet to be proven in a real world setting, however, and is hotly contested by some. Two projects currently under development may begin to resolve this debate: one at Heathrow Airport in London , scheduled to come into operation in ]; and another is planned at Dubai International Financial Center in Dubai scheduled to be operational in ].

]


==Overview== ==Overview==
Most ] systems move people in groups over scheduled routes. This has inherent inefficiencies.<ref name="ITNS November 2014">{{cite web|url=http://www.advancedtransit.org/wp-content/uploads/2011/08/ITNS-11-2014.pdf|title=An Intelligent Transportation Network System: Rationale, Attributes, Status, Economics, Benefits, and Courses of Study for Engineers and Planners|author=J. Edward Anderson|date=November 2014}}</ref> For passengers, time is wasted by waiting for the next vehicle to arrive, indirect routes to their destination, stopping for passengers with other destinations, and often confusing or inconsistent schedules. Slowing and accelerating large weights can undermine public transport's benefit to the environment while slowing other traffic.<ref name="ITNS November 2014" />
PRT has similarities to and differences from other forms of transport. To compare the proposed features:


Personal rapid transit systems attempt to eliminate these wastes by moving small groups nonstop in automated vehicles on fixed tracks. Passengers can ideally board a pod immediately upon arriving at a station, and can – with a sufficiently extensive network of tracks – take relatively direct routes to their destination without stops.<ref name="ITNS November 2014" /><ref>{{cite journal |last1=Ding |first1=Yida |last2=Wang |first2=Kai |last3=Zhang |first3=Lei |last4=Qu |first4=Xiaobo |title=Exploring the benefits of personal rapid transit in metropolitan area |journal=Communications in Transportation Research |date=2024 |volume=4 |pages=100117 |doi=10.1016/j.commtr.2023.100117 |doi-access=free}}</ref>
{| cellpadding="2" align="center" style="border:1px solid black;width:80%;"

|+ '''Comparison of Personal Rapid Transit (PRT) to existing transport systems'''
The low weight of PRT's small vehicles allows smaller guideways and support structures than mass transit systems like light rail.<ref name="ITNS November 2014" /> The smaller structures translate into lower construction costs, smaller ], and less visually obtrusive infrastructure.<ref name="ITNS November 2014" />
|-

|valign="top" align="right" style="padding:4px;"|'''Similar to ]s'''
As it stands, a citywide deployment with many lines and closely spaced stations, as envisioned by proponents, has yet to be constructed. Past projects have failed because of financing, cost overruns, regulatory conflicts, political issues, misapplied technology, and flaws in design, engineering or review.<ref name="ITNS November 2014" />
|style="border-bottom:solid 2px #fff;"|

* Vehicles are small -- typically 1 to 6 passengers.
However, the theory remains active. For example, from 2002 to 2005, the EDICT project, sponsored by the ], conducted a study on the feasibility of PRT in four European cities. The study involved 12 research organizations, and concluded that PRT:<ref name="EDICT">{{cite web |url=http://ec.europa.eu/research/environment/newsanddoc/article_2650_en.htm |title=Moving ahead with PRT |archiveurl=https://web.archive.org/web/20060921115952/http://ec.europa.eu/research/environment/newsanddoc/article_2650_en.htm |archivedate=2006-09-21 |website=ec.europa.eu}}</ref>
* Vehicles are individually hired, like taxis, and only shared with the passengers of one's choosing.
* would provide future cities "a highly accessible, user-responsive, environmentally friendly transport system which offers a sustainable and economic solution."
* Vehicles travel along a network of guideways, much like a network of streets. Routing is point-to-point, with no intermediate stops or transfers.
* could "cover its operating costs, and provide a return which could pay for most, if not all, of its capital costs."
* Can be available on an on-demand, around-the-clock basis.
* would provide "a level of service which is superior to that available from conventional public transport."
* would be "well received by the public, both public transport and car users."
The report also concluded that, despite these advantages, public authorities will not commit to building PRT because of the risks associated with being the first public implementation.<ref name="EDICT"/><ref name="EDICTFinalReport"> {{Webarchive|url=https://web.archive.org/web/20150526165330/http://archive.cardiff.gov.uk/traffic/internet/jondutton/edict/current/CONTENT/Del10%20-%20Final%20Report.pdf |date=2015-05-26 }} from cardiff.gov.uk</ref>

{| class="wikitable"
|+Comparison of personal rapid transit with existing transport systems
!style="text-align:left; vertical-align:top; padding:4px;"|Similar to cars / ]s
||
* Vehicles are small—typically two to six passengers
* Vehicles are individually hired, like taxis, and shared only with the passengers of one's choosing
* Vehicles travel along a network of guideways, much like a network of streets. Travel is point-to-point, with no intermediate stops or transfers
* Potential for on-demand, around-the-clock availability
* Stops are designed to be off the main guideway, allowing through traffic to bypass stations unimpeded
|- |-
|valign="top" align="right" style="padding:4px;"|'''Similar to ]s, ]es, and ]s''' ! style="text-align:left; vertical-align:top; padding:4px;"|Similar to ]s, ]es, and ]s
|| ||
* A public amenity, shared by multiple users. * A public amenity (although not necessarily publicly owned), shared by multiple users
* Reduced local pollution (electric powered). * Reduced local pollution (electric powered)
* Passengers embark and disembark at discrete stations analogous to ]s or ]s. * Passengers embark and disembark at discrete stations, analogous to ]s or ]s
|- |-
|valign="top" align="right" style="padding:4px;"|'''Similar to automated ]s''' ! style="text-align:left; vertical-align:top; padding:4px;"|Similar to automated ]s
|| ||
* Fully automated, including vehicle control, routing, and collection of fares. * Fully automated, including vehicle control, routing, and collection of fares
* Usually off-grade &mdash; typically elevated &mdash; reducing land usage and congestion. * Usually above the street—typically elevated—reducing land usage and congestion
|- |-
|valign="top" align="right" style="padding:4px;"|'''Distinct features''' ! style="text-align:left; vertical-align:top; padding:4px;"|Distinct features
|| ||
* Vehicle movements may be coordinated, unlike the autonomous human control of cars and bikes
* Stops can be along sidings, allowing thru traffic to bypass stations unimpeded.
* Small vehicle size allows infrastructure to be smaller than other transit modes
* Headway distance (the time between vehicles) is short &mdash; 2 seconds or less. Some PRT vehicles propose "platooning" their vehicles -- dynamically-recombining "trains" of vehicles, separated by a few inches, to reduce ] and increase speed, energy efficiency and passenger density.
* Automated vehicles can travel close together. Possibilities include dynamically combined "trains" of vehicles, separated by a few inches, to reduce ] and increase speed, energy efficiency and passenger density
|} |}

The PRT acronym was introduced formally in 1978 by ].<ref>J. Edward Anderson, {{Webarchive|url=https://web.archive.org/web/20060919102551/http://faculty.washington.edu/%7Ejbs/itrans/PRT/Background.html |date=2006-09-19 }}, University of Washington, 1978</ref> The ] (ATRA), a group which advocates the use of technological solutions to transit problems, compiled a definition in 1988 that can be seen here.<ref>{{cite web |url=http://faculty.washington.edu/jbs/itrans/PRT/Background.html |title=PRT Background |publisher=Faculty.washington.edu |access-date=2012-10-17 |archive-url=https://web.archive.org/web/20120728094847/http://faculty.washington.edu/jbs/itrans/PRT/Background.html |archive-date=2012-07-28 |url-status=dead }}</ref>

==List of operational automated transit networks (ATN) systems==
Currently, five advanced transit networks (ATN) systems are operational, and several more are in the planning stage.<ref>{{cite web|url=http://www.advancedtransit.org/advanced-transit/systems/|title=Advanced Transit & Automated Transport Systems|work=ATRA|access-date=2014-10-03|archive-date=2014-12-06|archive-url=https://web.archive.org/web/20141206015746/http://www.advancedtransit.org/advanced-transit/systems/|url-status=dead}}</ref>

{| class="wikitable sortable"
! System
! Manufacturer
! Type
! style="width: 180px;" | Locations
! Length
! width=100|{{nowrap|Stations / vehicles}}
! class="unsortable" | Notes
|-
| ]
| ]
| GRT
|
{{flagicon|United States}} ], US (1975)<ref name="Progressive Engineer">{{cite journal| last=Gibson| first=Tom| title=Still in a Class of Its Own| journal=Progressive Engineer| url=http://www.progressiveengineer.com/PEWebBackissues2002/PEWeb%2024%20Mar%2002-2/PRT.htm| access-date=2008-05-30| archive-url=https://web.archive.org/web/20120207004737/http://www.progressiveengineer.com/PEWebBackissues2002/PEWeb%2024%20Mar%2002-2/PRT.htm| archive-date=2012-02-07| url-status=dead}}</ref>
| {{convert|13.2|km|mi|1|abbr=on|sortable=on}}<ref name="WVU1"></ref>
| 5<ref name="WVU1" /> / 73<ref name="Progressive Engineer"/>
| Up to 20 passengers per vehicle, some rides not point-to-point during low usage periods<ref name="Progressive Engineer"/>
|-
| ]
|
| GRT
| {{flagicon|Netherlands}} Rivium, the Netherlands (November 2005)
| 1.8&nbsp;km (1.1&nbsp;mi)
| 5
| 2nd generation GRT (Group Rapid Transit) vehicles accommodate up to 24 passengers (12 seated). The vehicles operate on-schedule during peak hours, at a 2.5 minute interval, and can operate on demand during off-peak hours. The current system will operate until the end of 2018, after which it is expected to be replaced and expanded.<ref>{{cite web|title=RIVIUM GRT|url=https://www.2getthere.eu/projects/rivium-grt/|publisher=2getthere|access-date=1 September 2017|archive-url=https://web.archive.org/web/20170310200020/http://www.2getthere.eu/projects/rivium-grt/|archive-date=2017-03-10|url-status=dead}}. I pilot scheme operated on part of the current route between 1999 and 2005.</ref>{{needs update|date=March 2023}}
|-
| CyberCab
| <ref name="mogge1">Mogge, John, '','' "Figure 6. MASDAR Phase 1A Prototype Passenger PRT." Paper delivered at the , January 20, 2009. Available in WFES online media center.</ref>
| PRT
| {{flagicon|United Arab Emirates}} ], ], UAE (November 2010)
| {{convert|1.5|km|mi|1|abbr=on|sortable=on}}
| 2/10 passenger, (3/3 freight, not put into service)<ref>{{cite web|url = http://www.advancedtransit.org/wp-content/uploads/2011/08/PRT-Vehicle-Architecture-and-Control-in-Masdar-City-M.-de-Graaf.pdf|title=PRT Vehicle Architecture and Control in Masdar City}}</ref>
| Initial plans called for cars to be banned, with PRT as the only powered intra-city transport<ref name="panda">. World Wildlife Fund, January 13, 2008</ref> (along with an inter-city light rail line<ref name="intercity">). ''The Guardian'', January 21, 2008.</ref>). In October 2010 it was announced the PRT would not expand beyond the pilot scheme due to the cost of creating the undercroft to segregate the system from pedestrian traffic.<ref name="whymasdarscaleback"/><ref name="Masdarsinghub">{{cite web|url=http://singularityhub.com/2011/03/01/masdar-city-abandons-public-transportation-system-of-the-future|title=Masdar City Abandons Transportation System of the Future|work=Singularity HUB|date=March 2011}}</ref> Plans now include electric cars and electric buses.<ref>{{cite web |title= Masdar City - Sustainability and the City - Transportation |url= http://masdarcity.ae/en/62/sustainability-and-the-city/transportation/ |access-date= 2013-06-30 |archive-url= https://web.archive.org/web/20130713185713/http://masdarcity.ae/en/62/sustainability-and-the-city/transportation |archive-date= 2013-07-13 |url-status= dead }}</ref> In June 2013 a representative of the builder 2getthere said the freight vehicles had still not been put into service because they had not worked out how to get freight to and from the stations.<ref>{{cite web|title=Automated People Movers and Automated Transit Systems Conference|url=http://shanta-bonsall.com/?p=4|access-date=2013-07-28|archive-url=https://web.archive.org/web/20131029190129/http://shanta-bonsall.com/?p=4|archive-date=2013-10-29|url-status=dead}}</ref>
|-
| ]
| ]
| PRT
| {{flagicon|United Kingdom}} ], England, UK (June 2011)
| {{convert|3.8|km|mi|1|abbr=on|sortable=on}}<ref name="HeathrowBAA"> {{Webarchive|url=https://web.archive.org/web/20120228232730/http://www.baa.com/portal/controller/dispatcher.jsp?CiID=4a1d6acc2fce6110VgnVCM10000036821c0a____&ChID=b78aa08ae5c6d110VgnVCM10000036821c0a____&Ct=B2C_CT_PRESS_RELEASE&CtID=a22889d8759a0010VgnVCM200000357e120a____&ChPath=Home%5EBAA+Airports%5EPress+releases |date=2012-02-28 }}, 18 December 2007</ref>
| 3 / 21<ref name="HeathrowULTra">{{cite web |url=http://www.ultraprt.com/applications/existing-systems/heathrow/ |title=ULTra – ULTra at London Heathrow Airport |publisher=Ultraprt.com |access-date=2012-10-17 |url-status=dead |archive-url=https://web.archive.org/web/20100330100608/http://www.ultraprt.com/applications/existing-systems/heathrow/ |archive-date=2010-03-30 }}</ref>
| The Heathrow PRT system became operational in 2011, connecting Terminal 5 with a long-term car park.<ref name='heathrow-retail-travel'>{{cite web | url = http://www.heathrowairport.com/about-us/partners-and-suppliers/retail-travel-services | title = Heathrow Retail Travel Services | access-date = 2014-01-02 | quote = Heathrow Pod, began public service in 2011 and will carry around 500,000 passengers per year from the Terminal 5 business car park to the main terminal. | archive-date = 2014-01-02 | archive-url = https://web.archive.org/web/20140102194541/http://www.heathrowairport.com/about-us/partners-and-suppliers/retail-travel-services | url-status = dead }}</ref> In May 2014 ] said in a draft 5-year plan that it would extend the system throughout the airport, but this was dropped from the final plan.
|-
| Skycube<ref name="vecsuncheon">, Joong Ang Daily, 26 September 2009</ref>
| Vectus
| PRT
| {{flagicon|South Korea}} ], South Korea (September 2013)<ref name="vecsuncheon"/>
| {{convert|4.64|km|mi|1|abbr=on|sortable=on}}<ref>{{cite web |title = Korea's First Personal Rapid Transit (PRT), SkyCube |url = http://globalblog.posco.com/koreas-first-personal-rapid-transit-prt-skycube/ |access-date = 2014-09-08 |archive-date = 2014-09-08 |archive-url = https://web.archive.org/web/20140908132929/http://globalblog.posco.com/koreas-first-personal-rapid-transit-prt-skycube/ |url-status = dead }}</ref>
| 2 / 40<ref name="vecsuncheon"/>
| Connects the site of ] to a station in the wetlands "Buffer Area" next to the Suncheon Literature Museum;<ref>{{cite web| url=http://eng.2013expo.or.kr/?r=ENG&c=274/608&m=festivalmnm&front=view&type=CTS00700016&uid=74| title=Suncheon Literature Museum (pictorial map has representation of PRT connection)| access-date=2019-09-16| archive-url=https://web.archive.org/web/20181215122432/http://eng.2013expo.or.kr/?r=ENG&c=274%2F608&m=festivalmnm&front=view&type=CTS00700016&uid=74| archive-date=2018-12-15| url-status=dead}}</ref> the line runs parallel to the Suncheon-dong Stream.<ref>{{cite web| title = PRT System to Open for Suncheon Bay Garden Expo| date=12 February 2013| url=http://kojects.com/2013/02/13/prt-system-to-open-in-april-for-suncheon-bay-garden-expo/}}</ref> Stations are "on-line."
|-
| ]<!-- Operational? -->
| Kunming Shipbuilding Equipment<ref name=":0">{{Cite web |date=2021-04-07 |title=PRT项目无人小车进入批量调试阶段 |url=http://www.ksec.com.cn/view/kcmainpc/9/563/view/2414.html}}</ref>
|PRT
| {{Flagicon|CHN}} ], ], China
|{{Convert|5|km|mi|abbr=in}}
|3 / 22<ref name=":0" />
|
|}

==List of ATN suppliers==
{{main|List of automated transit networks suppliers}}
The following list summarizes several well-known automated transit networks (ATN) suppliers as of 2014, with subsequent amendments.<ref>{{cite web|url= http://transweb.sjsu.edu/PDFs/research/1227-automated-transit-networks.pdf |title=Automated Transit Networks(ATN): A Review of the Stateof the Industry and Prospectsfor the Future |date=15 November 2017 }}</ref>

* Revenue service: ] (]), ], , .
* Full test track: , ],<ref>{{cite web|url=http://faculty.washington.edu/jbs/itrans/cabin.htm |title=cabintaxi infopage |publisher=Faculty.washington.edu |date=2012-09-20 |access-date=2012-10-17}}</ref> ,
* Historical: ], ], PRT2000 (Raytheon),<ref>{{cite web|url=http://faculty.washington.edu/jbs/itrans/ray.htm |title=Raytheon's PRT 2000 infopage |publisher=Faculty.washington.edu |date=2002-08-18 |access-date=2013-11-24}}</ref> Monocab/], EcoMobility,<ref>{{cite journal |title=Analysis of dynamics of a scaled PRT (personal rapid transit) vehicle |year=2019 |url=https://www.jvejournals.com/article/20577 |journal=Journal of Vibroengineering |doi=10.21595/jve.2019.20577 |access-date=17 June 2021|last1=Kozłowski |first1=Maciej |volume=21 |issue=5 |pages=1426–1440 |s2cid=202090346 |doi-access=free }}</ref>


==History== ==History==


===Origins===
The concept originated with Don Fichter, a city transportation planner, and author of a 1964 book entitled "Individualized Automated Transit in the City".
Modern PRT concepts began around 1953 when Donn Fichter, a city transportation planner, began research on PRT and alternative transportation methods. In 1964, Fichter published a book<ref>{{citation
| author = Donn Fichter
| year = 1964
| title = Individualized Automatic Transit and the City
| publisher = B.H. Sikes, Chicago, IL, USA
}}</ref> which proposed an automated public transit system for areas of medium to low population density. One of the key points made in the book was Fichter's belief that people would not leave their cars in favor of public transit unless the system offered flexibility and end-to-end transit times that were much better than existing systems &ndash; flexibility and performance he felt only a PRT system could provide. Several other urban and transit planners also wrote on the topic and some early experimentation followed, but PRT remained relatively unknown.


Around the same time, Edward Haltom was studying ] systems. Haltom noticed that the time to start and stop a conventional large monorail train, like those of the ], meant that a single line could only support between 20 and 40 vehicles an hour. In order to get reasonable passenger movements on such a system, the trains had to be large enough to carry hundreds of passengers (see ] for a general discussion). This, in turn, demanded large guideways that could support the weight of these large vehicles, driving up capital costs to the point where he considered them unattractive.<ref name=a>Anderson</ref>
In the late ], the ], an independent non-profit corporation set up by Congress, spent substantial time and money on PRT, and performed much of the early theoretical and systems analysis. However this corporation is not allowed to sell to non-federal government customers. Members of the study team published in ] in ], the first wide-spread publication of the concept. The team subsequently published a text on PRT entitled ''Fundamentals of Personal Rapid Transit''<ref>{{cite web

| last = Irving
Haltom turned his attention to developing a system that could operate with shorter timings, thereby allowing the individual cars to be smaller while preserving the same overall route capacity. Smaller cars would mean less weight at any given point, which meant smaller and less expensive guideways. To eliminate the backup at stations, the system used "offline" stations that allowed the mainline traffic to bypass the stopped vehicles. He designed the ] system using six-passenger cars suspended on wheels from an overhead guideway. Like most suspended systems, it suffered from the problem of difficult switching arrangements. Since the car rode on a rail, switching from one path to another required the rail to be moved, a slow process that limited the possible headways.<ref name=a/>
| first = Jack

| coauthors = Harry Bernstein, C. L. Olson and Jon Buyan
===UMTA is formed===
| year = 1978
By the late 1950s the problems with ] were becoming evident in the United States. When cities improved roads and the transit times were lowered, suburbs developed at ever increasing distances from the city cores, and people moved out of the downtown areas. Lacking ] systems, the rapid rise in car ownership and the longer trips to and from work were causing significant air quality problems. Additionally, movement to the suburbs led to a ] from the downtown areas, one cause of the rapid ] seen in the US.
| url = http://faculty.washington.edu/jbs/itrans/irving.htm

| title = Fundamentals of Personal Rapid Transit
Mass transit systems were one way to combat these problems. Yet during this period, the federal government was feeding the problems by funding the development of the ], while at the same time funding for mass transit was being rapidly scaled back. Public transit ridership in most cities plummeted.<ref>Irving, pg. 1-2</ref>
| publisher = D.C. Heath and Company

| accessyear = 2006
In 1962, President ] charged ] with the task of addressing these problems. These plans came to fruition in 1964, when President ] signed the ] into law, thereby forming the ].<ref> {{webarchive|url=https://web.archive.org/web/20090827051813/http://www.fta.dot.gov/about/about_FTA_history.html |date=2009-08-27 }}, Federal Transit Administration</ref> UMTA was set up to fund mass transit developments in the same fashion that the earlier ] had helped create the Interstate Highways. That is, UMTA would help cover the capital costs of building out new infrastructure.

===PRT research starts===
However, planners who were aware of the PRT concept were worried that building more systems based on existing technologies would not help the problem, as Fitcher had earlier noted. Proponents suggested that systems would have to offer the flexibility of a car:

<blockquote>
The reason for the sad state of public transit is a very basic one – the transit systems just do not offer a service which will attract people away from their ]s. Consequently, their patronage comes very largely from those who cannot drive, either because they are too young, too old, or because they are too poor to own and operate an automobile. Look at it from the standpoint of a commuter who lives in a suburb and is trying to get to work in the ] (CBD). If he is going to go by transit, a typical scenario might be the following: he must first walk to the closest bus stop, let us say a five or ten minute walk, and then he may have to wait up to another ten minutes, possibly in inclement weather, for the bus to arrive. When it arrives, he may have to stand unless he is lucky enough to find a seat. The bus will be caught up in street congestion and move slowly, and it will make many stops completely unrelated to his trip objective. The bus may then let him off at a terminal to a suburban train. Again he must wait, and, after boarding the train, again experience a number of stops on the way to the CBD, and possibly again he may have to stand in the aisle. He will get off at the station most convenient to his destination and possibly have to transfer again onto a distribution system. It is no wonder that in those cities where ample inexpensive parking is available, most of those who can drive do drive.<ref>Irving, pg. 2</ref>
</blockquote>

In 1966, the ] was asked to "undertake a project to study ... new systems of urban transportation that will carry people and goods ... speedily, safely, without polluting the air, and in a manner that will contribute to sound city planning." The resulting report was published in 1968<ref>{{citation
| author = Leone M.Cole, Harold W. Merritt
| year = 1968
| title = Tomorrow's Transportation: New Systems for the Urban Future
| publisher = U.S. Department of Housing and Urban Development, Office of Metropolitan Development
}}</ref> and proposed the development of PRT, as well as other systems such as dial-a-bus and high-speed interurban links.

In the late 1960s, the ], an independent non-profit corporation set up by the US Congress, spent substantial time and money on PRT, and performed much of the early theoretical and systems analysis. However, this corporation is not allowed to sell to non-federal government customers. In 1969, members of the study team published the first widely publicized description of PRT in '']''.<ref>Systems Analysis of Urban Transportation Systems, ''Scientific American'', July 1969, Vol.221 No.1:19-27</ref>
In 1978 the team also published a book.<ref name="FundOfPRT">{{cite book
|last = Irving
|first = Jack
|author2 = Harry Bernstein
|author3 = C. L. Olson
|author4 = Jon Buyan
|year = 1978
|title = Fundamentals of Personal Rapid Transit
|publisher = D.C. Heath and Company
|url = http://www.advancedtransit.net/content/fundamentals-personal-rapid-transit-book
|access-date = 2023-06-11
|archive-url = https://web.archive.org/web/20080923093711/http://www.advancedtransit.net/content/fundamentals-personal-rapid-transit-book
|archive-date = 2008-09-23
|url-status = dead
}}</ref> These publications sparked off a sort of "transit race" in the same sort of fashion as the ], with countries around the world rushing to join what appeared to be a future market of immense size.

The ] made vehicle fuels more expensive, which naturally interested people in alternative transportation.

===System developments===
In 1967, aerospace giant ] started the ] in ]. After spending about 500 million ]s, the project was canceled when it failed its qualification trials in November 1987. The designers tried to make Aramis work like a "virtual train", but control software issues caused cars to bump unacceptably. The project ultimately failed.<ref>{{citation
| author = ]
| year = 1996
| title = Aramis, or the Love of Technology
| publisher = Harvard University Press
}}</ref> }}</ref>
.


Between 1970 and 1978, ] operated a project called "Computer-controlled Vehicle System" (CVS). In a full-scale test facility, 84 vehicles operated at speeds up to {{convert|60|km/h|mph|1}} on a {{convert|4.8|km|mi|1|adj=on|abbr=on}} guideway; one-second ]s were achieved during tests. Another version of CVS was in public operation for six months from 1975 to 1976. This system had 12 single-mode vehicles and four ]s on a {{convert|1.6|km|mi|1|adj=on|abbr=on}} track with five stations. This version carried over 800,000 passengers. CVS was cancelled when Japan's Ministry of Land, Infrastructure and Transport declared it unsafe under existing rail safety regulations, specifically in respect of braking and headway distances.
The ] project has been in continuous operation at ] in ] since ], with about 15,000 riders per day (]). The vehicles are rubber-tired and powered by electrified rails. Steam heating keeps the elevated guideway free of snow and ice. Most WVU students habitually use it. This system was not sold to other sites because the heated track has proven too expensive. The Morgantown system demonstrates automated control, but authorities no longer consider it a true PRT system. Its vehicles are too heavy and carry too many people, making it more similar to ] schemes. Most of the time it does not operate in a point to point fashion for individuals or small groups, running instead like an automated people mover or elevator from one end of the line to the other. It therefore has reduced capacity utilization compared to true PRT. Morgantown vehicles also weigh several tons and run on the ground for the most part, with higher land costs than other systems.


On March 23, 1973, U.S. Urban Mass Transportation Administration (UMTA) administrator Frank Herringer testified before Congress: "A DOT program leading to the development of a short, one-half to one-second headway, high-capacity PRT (HCPRT) system will be initiated in fiscal year 1974."<ref></ref> According to PRT supporter ], this was "because of heavy lobbying from interests fearful of becoming irrelevant if a genuine PRT program became visible." From that time forward people interested in HCPRT were unable to obtain UMTA research funding.<ref>{{cite web
The ] in ], by aerospace giant ], started in ], spent about 500 million francs, and was cancelled when it failed its qualification trials in November ]. The designers tried to make Aramis work like a "virtual train," but control software issues caused cars to bump unacceptably.
|url = http://www.reciprocalsystem.com/isus/articles/PRThistory.html
|title = The Historical Emergence and State-of-the-Art of PRT Systems
|author = J. Edward Anderson
|year = 1997
|access-date = 30 August 2017
|archive-url = https://web.archive.org/web/20170830233821/http://www.reciprocalsystem.com/isus/articles/PRThistory.html
|archive-date = 2017-08-30
|url-status = dead
}}</ref>


In 1975, the ] project was completed. It has five off-line stations that enable non-stop, individually programmed trips along an {{convert|8.7|mi|adj=on}} track serviced by a fleet of 71 cars. This is a crucial characteristic of PRT. However, it is not considered a PRT system because its vehicles are too heavy and carry too many people. When it carries many people, it operates in a point-to-point fashion, instead of running like an automated people mover from one end of the line to the other. During periods of low usage all cars make a full circuit stopping at every station in both directions. Morgantown PRT is still in continuous operation at ] in ], with about 15,000 riders per day ({{As of|2003|lc=on}}). The steam-heated track has proven expensive and the system requires an operation and maintenance budget of $5 million annually.<ref>{{cite web|url=http://www.governing.com/topics/transportation-infrastructure/personal-rapid-transit-system-morgantown-west-virginia.html|title=America's One and Only Personal Rapid Transit System|date=27 June 2011}}</ref> Although it successfully demonstrated automated control and it is still operating it was not sold to other sites. A 2010 report concluded replacing the system with buses on roads would provide unsatisfactory service and create congestion.<ref>{{cite web|title=PRT Facilities Master Plan|url=https://www.noexperiencenecessarybook.com/Exqg/prt-facilities-master-plan-west-virginia-university.html|publisher=Gannett Fleming|website=noexperiencenecessarybook|accessdate=4 September 2017|page=13|archive-date=4 September 2017|archive-url=https://web.archive.org/web/20170904065438/https://www.noexperiencenecessarybook.com/Exqg/prt-facilities-master-plan-west-virginia-university.html|url-status=dead}}</ref><ref>{{cite news|title=A Revolution That Didn't Happen: Personal Rapid Transit|url=https://www.npr.org/2016/10/03/494569967/a-revolution-that-didnt-happen-personal-rapid-transit|newspaper=NPR.org|accessdate=5 September 2017|date=3 October 2016}}</ref> Subsequently, the forty year old computer and vehicle control systems were replaced in the 2010s and there are plans to replace the vehicles.
A project called ''Computer-controlled Vehicle System'' (CVS) operated in Japan from 1970 to c.1978. In a full scale test facility, 84 vehicles operated at speeds up to 60 km/h on a 4.8 km guideway; 1 second headways were achieved during tests. Another version of CVS was in public operation for six months during 1975-76. This system had 12 single-mode vehicles and 4 dual-mode vehicles on a one mile track with five stations. This version had over 800,000 passengers. CVS was cancelled when Japan's Ministry of Land, Infrastructure and Transport adjudged it unsafe under existing rail safety regulations, specifically in respect of braking and headway distances.


In ], the '']'' project, a joint venture from Mannesmann Demag and ], created an extensive PRT development in the 1970-80s considered fully developed by the German Government and its safety authorities. This project was canceled when a disagreement over the site for the initial implementation coincided with non-defense budget cuts by the German government. From 1969 to 1980, Mannesmann Demag and ] cooperated to build the '']'' urban transportation system in ]. Together the firms formed the Cabintaxi Joint Venture. They created an extensive PRT technology, including a test track, that was considered fully developed by the German government and its safety authorities. The system was to have been installed in ], but budget cuts stopped the proposed project before the start of construction. With no other potential projects on the horizon, the joint venture disbanded, and the fully developed PRT technology was never installed. Cabintaxi Corporation, a US-based company, obtained the technology in 1985, and remains active in the private-sector market trying to sell the system but so far there have been no installations.


In 1979 the three station ] system was commissioned. Uniquely, the cars could move sideways, as well as backwards and forwards and it was described as a "horizontal elevator". The system was closed in 2009 to allow for expansion of the hospital.
] invested heavily in a system called PRT2000 in the ], and failed to install a contracted system in Rosemont, near Chicago, when its estimated costs exceeded $50,000,000 per mile. This system may be available for sale by York PRT. In 2000, rights to the technology reverted to the ], and were purchased by Taxi2000.


In the 1990s, ] invested heavily in a system called PRT 2000, based on technology developed by ] at the ]. Raytheon failed to install ] in ], near ], when estimated costs escalated to ]50 million per mile, allegedly due to design changes that increased the weight and cost of the system relative to Anderson's original design. In 2000, rights to the technology reverted to the University of Minnesota, and were subsequently purchased by Taxi2000.<ref>{{citation
The ] project proposes using ] in solid-state vehicles to achieve speeds of 100 mph (161 km/h).
| author = Peter Samuel
| year = 1996
| title = Status Report on Raytheon's PRT 2000 Development Project
| publisher = ITS International
}}</ref><ref>{{citation
| author = Peter Samuel
| year = 1999
| title = Raytheon PRT Prospects Dim but not Doomed
| publisher = ITS International
}}</ref>


===Later developments===
In ], 2getthere, a consortium of Frog Navigation Systems and Yamaha, operated "CyberCabs" at Holland's 2002 ] festival. These transported passengers up to 1.2 km on Big Spotters Hill. CyberCab is like a ], except it steers itself using magnet guidance points embedded in the lane.
In 1999 the 2getthere designed ] system was opened in the Kralingen neighbourhood of eastern Rotterdam using 12-seater driverless buses. The system was extended in 2005 and new second-generation vehicles introduced to serve five stations over {{convert|1.8|km|mi}} with five grade crossings over ordinary roads. Operation is scheduled in peak periods and on demand at other times.<ref>{{cite web|title=RIVIUM GRT|url=https://www.2getthere.eu/projects/rivium-grt/|publisher=2getthere|access-date=1 September 2017|archive-url=https://web.archive.org/web/20170310200020/http://www.2getthere.eu/projects/rivium-grt/|archive-date=2017-03-10|url-status=dead}}</ref> In 2002, 2getthere operated twenty five 4-passenger "CyberCabs" at Holland's 2002 ] horticultural exhibition. These transported passengers along a track spiraling up to the summit of Big Spotters Hill. The track was approximately {{convert|600|m|ft|0|adj=on}} long (one-way) and featured only two stations. The six-month operation was intended to research the public acceptance of PRT-like systems.


In 2010 a 10-vehicle (four seats each), two station 2getthere system was opened to connect a parking lot to the main area at ], UAE. The systems runs in an undercroft beneath the city and was supposed to be a pilot project for a much larger network, which would also have included transport of freight. Expansion of the system was cancelled just after the pilot scheme opened due to the cost of constructing the undercroft and since then other electric vehicles have been proposed.<ref name="whymasdarscaleback">{{cite web|title= Why Has Masdar Personal Rapid Transit (PRT) Been Scaled Back?|url= http://www.prtconsulting.com/blog/index.php/2010/10/16/why-has-masdar-personal-rapid-transit-prt-been-scaled-back/|url-status= dead|archive-url= https://web.archive.org/web/20131213234856/http://www.prtconsulting.com/blog/index.php/2010/10/16/why-has-masdar-personal-rapid-transit-prt-been-scaled-back/|archive-date= 2013-12-13}}</ref>
In ], Ford Research proposed a ] system called PRISM. It would use public guideways with privately-purchased but certified dual-mode vehicles. The vehicles would be less than 600 kg (1200 lb), allowing small elevated guideways which could use centralized computer controls and power.


In January 2003, the prototype ] ("Urban Light Transport") system in ], Wales, was certified to carry passengers by the UK Railway Inspectorate on a {{convert|1|km|mi|1|abbr=on|adj=on}} test track. ULTra was selected in October 2005 by ] for London's ].<ref> {{webarchive|url=https://web.archive.org/web/20090211201500/http://www.heathrowairport.com/portal/controller/dispatcher.jsp?CiID=724474cd82a07010VgnVCM10000036821c0a____&CtID=a22889d8759a0010VgnVCM200000357e120a____&Ct=B2C_CT_PRESS_RELEASE&ChPath=Corporate%5EMedia%20Centre%5ENews%20Releases%5EResults |date=2009-02-11 }} BAA plc Press Release - 20 October 2005</ref> Since May 2011 a three-station system has been open to the public, transporting passengers from a remote parking lot to terminal 5.<ref name="HeathrowBAA" /> During the deployment of the system the owners of Heathrow became owners of the UltrPRT design. In May 2013 Heathrow Airport Limited included in its draft five-year (2014–2019) master plan a scheme to use the PRT system to connect terminal 2 and terminal 3 to their respective business car parks. The proposal was not included in the final plan due to spending priority given to other capital projects and has been deferred.<ref>{{cite journal| title=My Pods| journal=Futureairports| volume=2014| issue=1| pages=61| url=http://viewer.zmags.com/publication/b0ecc6ab#/b0ecc6ab/1| access-date=8 September 2014}}</ref> If a third runway is constructed at Heathrow will destroy the existing system, which will be built over, will be replaced by another PRT.
In January ], a prototype ULTra ("Urban Light Transport") system from Advanced Transport Systems Ltd in ] was certified to carry passengers by the UK Rail Inspectorate on a 1 km test track. It had successful passenger trials and has met all project milestones for time and cost. The ULTra system differs from many other systems in its focus on using off-the-shelf technology and rubber tires running on an open guideway. This approach has resulted in a system that is more economical than designs requiring custom technology.


In June 2006, a Korean/Swedish consortium, Vectus Ltd, started constructing a {{convert|400|m|ft|0|adj=on|abbr=on}} test track in ], Sweden.<ref>{{cite web | year = 2006 | url = http://kinetic.seattle.wa.us/nxtlevel/prt/vectusnews.html | title = Vectus News | publisher = Vectus Ltd. | access-date = 31 December 2007 | url-status = dead | archive-url = https://web.archive.org/web/20070929083346/http://kinetic.seattle.wa.us/nxtlevel/prt/vectusnews.html | archive-date = 29 September 2007 }}</ref> This test system was presented at the 2007 PodCar City conference in Uppsala.<ref> from podcar.org</ref> A 40-vehicle, 2-station, {{convert|4.46|km|mi|1|abbr=on}} system called "SkyCube" was opened in ], South Korea, in April 2014.<ref>{{cite web| title=Korea's First Personal Rapid Transit (PRT), SkyCube| url=http://globalblog.posco.com/koreas-first-personal-rapid-transit-prt-skycube/| date=April 30, 2014| access-date=September 8, 2014| archive-date=September 8, 2014| archive-url=https://web.archive.org/web/20140908132929/http://globalblog.posco.com/koreas-first-personal-rapid-transit-prt-skycube/| url-status=dead}}</ref>
ULTra was recently (October, 2005) selected] by ] for London's ]. This system is planned to transport 11,000 passengers per day from remote parking lots to the central terminal area. PRT is favored because of zero on-site emissions from the electrically powered vehicles. PRT will also increase the capacity of existing tunnels without enlargement. BAA plans begin operation by the end of 2007 and to expand the system in 2009.


In the 2010s the Mexican ] began research into project LINT ("Lean Intelligent Network Transportation") and built a 1/12 operational scale model.<ref>{{cite web|title=Proyecto LINT|url=https://www.youtube.com/watch?v=r7L7zuB-tMU| archive-url=https://ghostarchive.org/varchive/youtube/20211211/r7L7zuB-tMU| archive-date=2021-12-11 | url-status=live|website=YouTube|publisher=ITESO Instituto Tecnológico y de Estudios Superiores de Occidente|access-date=30 August 2017}}{{cbignore}}</ref> This was further developed and became the Modutram<ref></ref> system and a full-scale test track was built in ], which was operational by 2014.<ref>{{cite web|title=ModuTram Test Track|date=19 February 2014|url=http://www.advancedtransit.org/library/news/modutram-test-track/|publisher=Advanced Transit Association|access-date=30 August 2017}}</ref>
Vectus Ltd., a Korean/Swedish consortium, is constructing (2006) a test track in Sweden.


In 2018 it was announced that a PRT system would be installed at the new ].<ref name="jqknews.com"/> The system will include 6 miles of guideway, 4 stations, 22 pods and will connect airport parking to two terminal buildings. It is supplied by Ultra MTS. The airport is due to open in 2021.<ref>{{cite web |title=Chengdu Tianfu International Airport PRT System |url=https://myemail.constantcontact.com/Chengdu-Tianfu-International-Airport-PRT-System.html?soid=1102621083285&aid=rcfapCSHK4I |website=ATRA Pulse |publisher=ATRA |access-date=10 June 2021}}</ref>
==PRT System Design==
There are currently no agreed-upon standards in PRT system design. Among the handful of PRT systems that are currently developing hardware -- and the many dozens of PRT designs that exist on paper -- there is a tremendous diversity of design approaches. Not only are the designs diverse, they are also in many cases quite contentious. The following sections provide an overview of the primary different design approaches, and highlights the major disputes, where they occur.


===Vehicle Design=== ==System design==
Among the handful of prototype systems (and the larger number that exist on paper) there is a substantial diversity of design approaches, some of which are controversial.
====Capacity====
Vehicle size is one of the most important aspects of PRT system design. Larger vehicles are more expensive to produce, require more energy to move, and require bulkier infrastructure to support. Therefore, PRT designers attempt to design for the smallest practical vehicle. This is controversial: critics of PRT claim that smaller vehicles reduce the overall passenger capacity of any transit system. PRT designers respond that this is only true if long headway distances are assumed (see below), and that any reduction in vehicle capacity can be offset by an increase in the number of vehicles, and a decrease in the headway distances between them.


===Vehicle design===
Critical to the question of vehicle size is the average number of passengers that would actually ride in each vehicle. Until a public PRT system is constructed, this cannot be known for certain, and must be estimated. Since PRT uses a fundamentally different system design than other mass transit systems, ridership cannot be extrapolated from fixed-route systems such as buses or trains. The obvious precedent for personal point-to-point travel is the private automobile, which in commuter areas in the U.S. average 1.16 persons per vehicle. This has led some PRT designers to claim that the optimum vehicle size is 2 passengers (or less). Some systems (notably UniModal / Skytran) have been designed this way, resulting in extremely compact and lightweight vehicles and infrastructure. However, other PRT designers believe that larger vehicles are necessary, to accommodate handicapped passengers, as well as families traveling together. As of 2006, all PRT systems which are known to be under active development (ULTra, Vectus, Skyweb, Taxi 2000) use 4-passenger vehicles.
Vehicle weight influences the size and cost of a system's guideways, which are in turn a major part of the capital cost of the system. Larger vehicles are more expensive to produce, require larger and more expensive guideways, and use more energy to start and stop. If vehicles are too large, point-to-point routing also becomes more expensive. Against this, smaller vehicles have more surface area per passenger (thus have higher total air resistance which dominates the energy cost of keeping vehicles moving at speed), and larger motors are generally more efficient than smaller ones.


The number of riders who will share a vehicle is a key unknown. In the U.S., the average car carries 1.16 persons,<ref>Skytran Web Site: See "common sense"</ref> and most industrialized countries commonly average below two people; not having to share a vehicle with strangers is a key advantage of ]. Based on these figures, some have suggested that two passengers per vehicle (such as with ], EcoPRT and Glydways), or even a single passenger per vehicle is optimum. Other designs use a car for a model, and choose larger vehicles, making it possible to accommodate families with small children, riders with bicycles, disabled passengers with wheelchairs, or a ] or two of freight.
If PRT vehicles are too large, then point-to-point routing becomes uneconomical, as most vehicles would be highly under-utilized. For example, when the PRT system at West Virginia University grew from a 6-passenger to a 20-passenger vehicles, point-to-point operations were largely abandoned.


====Propulsion==== ====Propulsion====
All current designs (except for the human-powered ]) are powered by ]. In order to reduce vehicle weight, power is generally transmitted via lineside conductors although two of the operating systems use on-board batteries. According to the designer of Skyweb/Taxi2000, ], the lightest system uses ] (LIM) on the vehicle for both propulsion and braking, which also makes manoeuvres consistent regardless of the weather, especially rain or snow. LIMs are used in a small number of rapid transit applications, but most designs use ]s. Most such systems retain a small on-board battery to reach the next stop after a power failure. CabinTaxi uses a LIM and was able to demonstrate 0.5 second headways on its test track. The Vectus prototype system used continuous track mounted LIMs with the reaction plate on the vehicle, eliminating the active propulsion system (and power required) on the vehicle.
PRT vehicles are powered by ]. Most systems plan multiply-redundant power supplies, from track-side batteries or natural-gas-powered generators. Stationary power reduces the vehicles' weight.


] and 2getthere use on-board batteries, recharged at stations. This increases the safety, and reduces the complexity, cost and maintenance of the guideway. As a result, the ULTRa guideway resembles a sidewalk with curbs and is inexpensive to construct. ULTRa and 2getthere vehicles resembles small automated electric cars, and use similar components. (The ULTRa POD chassis and cabin have been used as the basis of a shared autonomous vehicle for running in mixed traffic.<ref>{{cite news |title=Westfield Technology Group autonomous POD confirmed for Fleet Live 2019 |url=https://www.fleetnews.co.uk/news/fleet-industry-news/2019/08/01/westfield-technology-group-autonomous-pod-confirmed-for-fleet-live-2019 |access-date=28 June 2021 |date=1 August 2019 |archive-date=28 June 2021 |archive-url=https://web.archive.org/web/20210628030728/https://www.fleetnews.co.uk/news/fleet-industry-news/2019/08/01/westfield-technology-group-autonomous-pod-confirmed-for-fleet-live-2019 |url-status=dead }}</ref>)
According to designer of Skyweb/Taxi2000 J.E. Anderson (below), the lightest-weight system, and therefore the one with the lowest system cost, is a ] (LIM) on the car, thrusting against a stationary conductive rail for both propulsion and braking. Loss of traction due to precipitation, ice or sudden braking is therefore not an issue, since a LIM's magnetic interaction with the rail would be unaffected. This aspect contributes to the feasibility of short headways between PRT vehicles. LIMs also minimize the number of moving parts in the car, reducing maintenance costs, and lowers the relative fabrication expense for the rail. It's also easy for an on-board computer to control. A similar system was proposed by Doug Malewicki for Skytran.

The ] and ULTra systems use off-the-shelf rotary electric motors. Matra used a "variable reluctance motor" in Aramis.


====Switching==== ====Switching====
Almost all designs avoid ], instead advocating vehicle-mounted switches (which engage with special guiderails at the junctions) or conventional steering. Advocates say that vehicle-switching permits faster routing so vehicles can run closer together which increases capacity. It also simplifies the guideway, makes junctions less visually obtrusive and reduces the impact of malfunctions, because a failed switch on one vehicle is less likely to affect other vehicles.
Most designers eschew ] (or points) built into the track because failure of an in-track switch would degrade capacity. Vehicle-mounted switches are preferred so that tracks stay in service, and to allow closer spacing of vehicles since no time delay is needed to allow the track to switch. Alternatively, the vehicles may have more conventional steering.


Track switching greatly increases headway distance. A vehicle must wait for the previous vehicle to clear the junction, for the track to switch and for the switch to be verified. Communication between the vehicle and wayside controllers adds both delays and more points of failure. If the track switching is faulty, vehicles must be able to stop before reaching the switch, and all vehicles approaching the failed junction would be affected.
===Infrastructure Design===
====Guideways====
There is some debate over the best guideway for PRT systems. No standard has been agreed and guideways in proposed systems may be incompatible with both each other and existing transportation technologies. Some points of agreement exist: guideways should permit fast switching and effective braking, be inexpensive, be capable of being built at ground level or elevated, and not visually intrusive. Ideally they should not need to be cleared of dust or snow. Most systems would also use the guideway to distribute power, data, and routing indications to the vehicles.


Mechanical vehicle switching minimizes inter-vehicle spacing or headway distance, but it also increases the minimum distances between consecutive junctions. A mechanically switching vehicle, maneuvering between two adjacent junctions with different switch settings, cannot proceed from one junction to the next. The vehicle must adopt a new switch position, and then wait for the in-vehicle switch's locking mechanism to be verified. If the vehicle switching is faulty, that vehicle must be able to stop before reaching the next switch, and all vehicles approaching the failed vehicle would be affected.
Structurally, some guideway designs are similar to monorail beams, several are bridge-like trusses supporting internal tracks, and others are just cables embedded in a conventional or narrow roadway that can be elevated. An elevated track structure scales down dramatically with lower vehicle weights. Therefore, the vehicle's weight budget is critical. The heavier the vehicle, the more costly the track, and the track is the gating system cost. As well, large tracks are visually intrusive, so small vehicles contribute to a more attractive track.


Conventional steering allows a simpler 'track' consisting only of a road surface with some form of reference for the vehicle's steering sensors. Switching would be accomplished by the vehicle following the appropriate reference line – maintaining a set distance from the left roadway edge would cause the vehicle to diverge left at a junction, for example.
Most designs put the vehicle on top of the track, which reduces visual intrusion and cost, as well as allowing low cost ground-level installation, and allow simpler track switching. Overhead suspended vehicles are said to unload the skins of the vehicle, which can therefore be lighter - many materials are stronger in tension than they are in compression. An overhead track is necessarily higher, and therefore more visible, but also narrower, and therefore creates less shadow, while having a small silhouette.


===Infrastructure design===
Fast, reliable switching is a key requirement for PRT that rules out some designs. For example, in most monorails, the rail is so heavy that the switch movement time would increase the time between PRT cars so much that the guideway is no longer competitive with a bus.
]


====Guideways====
Some PRT systems have had substantial extra expenses from the extra track needed to decelerate and accelerate from the numerous stations. In at least one system, Aramis, this nearly doubled the width and expense of the required right-of-way, and caused the nonstop passenger delivery concept to be abandoned. Other systems have schemes to reduce this cost. Control algorithms can space vehicles to reduce siding lengths (see below). Elevated tracks can also "vertically merge" and keep to a narrow right of way.
Several types of guideways have been proposed or implemented, including beams similar to monorails, bridge-like ]es supporting internal tracks, and cables embedded in a roadway. Most designs put the vehicle on top of the track, which reduces visual intrusion and cost, as well as easing ground-level installation. An overhead track is necessarily higher, but may also be narrower. Most designs use the guideway to distribute power and data communications, including to the vehicles. The ] failed its cost targets because of the steam-heated track required to keep the large channel guideway free of frequent snow and ice. Heating uses up to four times as much as energy as that used to propel the vehicles.<ref>{{cite web |title=The History of my Involvement in PRT and how it led to ATRA |url=https://www.inist.org/library/2019-10.Anderson.History%20of%20my%20involvement%20in%20PRT%20led%20to%20ATRA.pdf |website=INIST |access-date=3 July 2021 |archive-date=9 July 2021 |archive-url=https://web.archive.org/web/20210709185013/https://www.inist.org/library/2019-10.Anderson.History%20of%20my%20involvement%20in%20PRT%20led%20to%20ATRA.pdf |url-status=dead }}</ref> Most proposals plan to resist snow and ice in ways that should be less expensive. The Heathrow system has a special de-icing vehicle. Masdar's system has been limited because the exclusive right-of-way for the PRT was gained by running the vehicles in an undercroft at ground-level while building an elevated "street level" between all the buildings. This led to unrealistically expensive buildings and roads.<ref name="whymasdarscaleback"/>


====Stations==== ====Stations====
Embarkation stations are on sidings so that through traffic can bypass vehicles picking up or dropping off passengers. Each station might have multiple berths, with perhaps 1/3 of the vehicles in a system being stored at stations waiting for passengers. Proposals usually have stations close together, and located on side tracks so that through traffic can bypass vehicles picking up or dropping off passengers. Each station might have multiple berths, with perhaps one-third of the vehicles in a system being stored at stations waiting for passengers. Stations are envisioned to be minimalistic, without facilities such as rest rooms. For elevated stations, an elevator may be required for accessibility.


At least one system, Metrino, provides wheelchair and freight access by using a cogway in the track, so that the vehicle itself can go from a street-level stop to an overhead track.
Embarkation stations can be small, inexpensive, and should not require amenities such as seating or restrooms. Stations may be elevated to guideway level, or be sited inside buildings or at street level.


Some designs have included substantial extra expense for the track needed to decelerate to and accelerate from stations. In at least one system, Aramis, this nearly doubled the width and cost of the required right-of-way and caused the nonstop passenger delivery concept to be abandoned. Other designs have schemes to reduce this cost, for example merging vertically to reduce the footprint.
===Operational Characteristics===
====Headway Distance====
The spacing of PRT vehicles on the guideway defines the maximum passenger capacity of the system. Designers therefore attempt to minimize the ''headway,'' the distance between vehicles. Some have planned for very short headways. Capacities are stated to be equivalent to or greater than light rail. Computerized control permits closer spacing than the two-second headways recommended for cars without degrading safety, since all cars can be braked simultaneously.


===Operational characteristics===
Very short headways are controversial. Some regulators (e.g. the British Rail inspectorate, regulating ULTra) are willing to accept two second headways. In these systems, a PRT guideway carries the same number of passenger-miles as a lane of freeway traffic. Regulators may be willing to reduce headways with increased operational PRT experience, achieving passenger densities perhaps four times that of a freeway lane.


====Headway distance====
Rail regulations legally apply to PRT systems in some places (See CVS, above); rail regulators may calculate headways in terms of absolute stopping distances, as is traditional in heavy rail. This may make PRT systems uneconomical.
Spacing of vehicles on the guideway influences the maximum passenger capacity of a track, so designers prefer smaller ] distances. Computerized control and active electronic braking (of motors) theoretically permit much closer spacing than the two-second headways recommended for cars at speed. In these arrangements, multiple vehicles operate in "platoons" and can be braked simultaneously. There are prototypes for ] based on similar principles.


Very short headways are controversial. The UK Railway Inspectorate has evaluated the ULTra design and is willing to accept one-second headways, pending successful completion of initial operational tests at more than 2 seconds.<ref></ref> In other jurisdictions, preexisting rail regulations apply to PRT systems (see CVS, above); these typically calculate headways for absolute stopping distances with standing passengers. These severely restrict capacity and make PRT systems infeasible. Another standard said trailing vehicles must stop if the vehicle in front stopped instantaneously (or like a "brick wall"). In 2018 a committee of the ] considered replacing the "brick wall" standard with a requirement for vehicles to maintain a safe "separation zone" based on the minimum stopping distance of the lead vehicle and the maximum stopping of the trailing vehicle.<ref>{{cite web |title=ASCE APM STANDARDS COMMITTEE ACCEPTS ALTERNATIVE TO BRICK WALL STOP |url=http://www.advancedtransit.org/library/news/asce-apm-standards-committee-accepts-alternative-brick-wall-stop/ |website=Advanced Transit |date=11 May 2018 |access-date=3 July 2021}}</ref> These changes were introduced into the standard in 2021.
====Capacity Utilization====
Due to lack of full-scale installations all capacity utilization calculations are based on simulation and modelling, and are therefore contested by those skeptical of PRT.


====Capacity====
In theory, if the peak speeds of PRT and a train were the same, the PRT should be two to three times faster, simply because the PRT vehicles do not stop every few hundred yards to let passengers on and off, yielding two to three times as many trips per seat as a bus or train.
PRT is usually proposed as an alternative to rail systems, so comparisons tend to be with rail. PRT vehicles seat fewer passengers than trains and buses, and must offset this by combining higher average speeds, diverse routes, and shorter headways. Proponents assert that equivalent or higher overall capacity can be achieved by these means.


=====Single line capacity=====
PRT systems could also automatically divert vehicles to busy routes, and travel nonstop at maximum speeds. Simulations suggest that at these speeds vehicles can be recycled for new trips as often as several times per hour, even during busy periods and low-density cities. In simulations of rush hour or high-traffic events about 1/3 of vehicles on the guideway need to be empty to minimize response time. It is also stated that higher speeds should allow a smaller fleet to serve the same number of passengers.
With two-second headways and four-person vehicles, a single PRT line can achieve theoretical maximum capacity of 7,200 passengers per hour. However, most estimates assume that vehicles will not generally be filled to capacity, due to the point-to-point nature of PRT. At a more typical average vehicle occupancy of 1.5 persons per vehicle, the maximum capacity is 2,700 passengers per hour. Some researchers have suggested that rush hour capacity can be improved if operating policies support ridesharing.<ref>{{cite web
| url = http://pubsindex.trb.org/document/view/default.asp?lbid=803547
| title = Doubling Personal Rapid Transit Capacity with Ridesharing
| last = Johnson | first = Robert E.
| year = 2005 | access-date = August 30, 2017
| work = Transportation Research Record: Journal of the Transportation Research Board, No. 1930
}}</ref>


Capacity is inversely proportional to headway. Therefore, moving from two-second headways to one-second headways would double PRT capacity. Half-second headways would quadruple capacity. Theoretical minimum PRT headways would be based on the mechanical time to engage brakes, and these are much less than a half second. Researchers suggest that high capacity PRT (HCPRT) designs could operate safely at half-second headways, which has already been achieved in practice on the Cabintaxi test track in the late 1970s.<ref>{{cite web
====Control Algorithms====
| url = http://faculty.washington.edu/jbs/itrans/big/soa2.pdf
One algorithm places vehicles in imaginary moving "slots" that go around the loops of track, analogous to ] networking. Real vehicles are allocated a slot by track-side controllers. On-board computers maintain their position by using a ] to stay near the center of the commanded slot. One way vehicles can keep track of their position is by integrating the input from speedometers, using periodic check points to compensate for cumulative errors.
| title = Emerging Personal Rapid Transit Technologies
| last = Buchanan | first = M. |author2=J.E Anderson |author3=G. Tegnér |author4=L. Fabian
| author5=J. Schweizer
| year = 2005 | access-date = August 30, 2017
| work = Proceedings of the AATS conference, Bologna, Italy, 7–8 November 2005
}}</ref> Using the above figures, capacities above 10,000 passengers per hour seem in reach.


In simulations of rush hour or high-traffic events, about one-third of vehicles on the guideway need to travel empty to resupply stations with vehicles in order to minimize response time. This is analogous to trains and buses travelling nearly empty on the return trip to pick up more rush hour passengers.
Another style of algorithm assigns a trajectory to a vehicle, after verifying that the trajectory does not violate the safety margins of other vehicles. This system permits system parameters to be adjusted to design or operating conditions. may use use slightly less energy.


] light rail systems can move 15,000 passengers per hour on a fixed route, but these are usually fully grade separated systems. Street level systems typically move up to 7,500 passengers per hour. Heavy rail subways can move 50,000 passengers per hour per direction. As with PRT, these estimates depend on having enough trains.
The maker of the ULTra PRT system reports that testing of its control system shows lateral (side-to-side) accuracy of 1 cm, and docking accuracy better than 2 cm.


Neither light nor heavy rail scales operated efficiently in off-peak when capacity utilization is low but a schedule must be maintained. In a PRT system when demand is low, surplus vehicles will be configured to stop at empty stations at strategically placed points around the network. This enables an empty vehicle to quickly be despatched to wherever it is required, with minimal waiting time for the passenger. PRT systems will have to re-circulate empty vehicles if there is an imbalance in demand along a route, as is common in peak periods.
====Ridership Attraction====
Ridership simulations with standard assumptions show that PRT, which should be substantially faster than autos in areas with traffic jams, would attract between 35% and 60% of automobile users. This is significantly larger than typical ridership of other public transit modes, both in reality and in simulation.


=====Networked PRT capacity=====
Some PRT systems (See Unimodal) plan speeds substantially faster than automobiles achieve on ''empty'' expressways. In simulations, these attract even more traffic than slower, conservative PRT designs. If true, the high riderships would substantially decrease the cost per rider of PRT compared to trains and buses.
The above discussion compares line or ] and may therefore not be relevant for a networked PRT system, where several parallel lines (or parallel components of a grid) carry traffic. In addition, Muller estimated<ref>{{Cite web |url=http://www.leighfisher.com/trb/657-2-05-0599.pdf |title=Muller et al. TRB |access-date=2006-09-25 |archive-url=https://web.archive.org/web/20060831081723/http://www.leighfisher.com/trb/657-2-05-0599.pdf |archive-date=2006-08-31 |url-status=dead }}</ref> that while PRT may need more than one guideway to match the capacity of a conventional system, the capital cost of the multiple guideways may still be less than that of the single guideway conventional system. Thus comparisons of line capacity should also consider the cost per line.


PRT systems should require much less horizontal space than existing metro systems, with individual cars being typically around 50% as wide for side-by-side seating configurations, and less than 33% as wide for single-file configurations. This is an important factor in densely populated, high-traffic areas.
====Safety====
] at PRT companies assert that travel via PRT systems should be much safer than public roads. Computer control is considered more reliable than drivers. Grade-separated guideways prevent collisions with pedestrians or manually-controlled vehicles. Most PRT systems enclose the running gear in the guideway to prevent derailments. Vehicles usually have computer-diagnosed, dual-redundant motors and electronics.


====Travel speed====
The Morgantown system, which is more correctly described as an "Automated Guideway Transit" system (AGT) has now completed 110 million passenger-miles without serious injury. However, according to the U.S. Department of Transportation, AGT systems as a group have higher injury rates than any other form of rail-based transit (subway, metro, light rail, or commuter rail). Still, as a result of total grade-separation, AGT systems are safer than ordinary buses or automobiles.
For a given peak speed, nonstop journeys are about three times as fast as those with intermediate stops. This is not just because of the time for starting and stopping. Scheduled vehicles are also slowed by boardings and exits for multiple destinations.


Therefore, a given PRT seat transports about three times as many passenger miles per day as a seat performing scheduled stops. So PRT should also reduce the number of needed seats threefold for a given number of passenger miles.
As with many current transit systems, safety concerns are likely to be addressed through grade separation (elevated tracks and/or dedicated right-of-ways), CCTV monitoring, and communication with a central command center from which engineering or other assistance may be requested.


While a few PRT designs have operating speeds of {{convert|100|km/hour|mph|abbr=on}}, and one as high as {{convert|241|km/hour|mph|abbr=on}},<ref>The concept-level SkyTran system is proposed to travel at up to </ref> most are in the region of {{convert|40-70|km/hour|mph|abbr=on}}. Rail systems generally have higher maximum speeds, typically {{convert|90-130|km/hour|mph|abbr=on}} and sometimes well in excess of {{convert|160|km/hour|mph|abbr=on}}, but average travel speed is reduced about threefold by scheduled stops and passenger transfers.
===Cost Characteristics===
Estimates of guideway cost range between $0.8 million and $22 million per mile.<ref>{{cite web
| year = ]
| url = http://advancedtransit.org/%5Cpub%5C2002%5Cprt%5Ctech6.pdf
| title = Personal Automated Transportation: Status and Potential of Personal Rapid Transit, p.89
| publisher = Advanced Transit Association
| format = PDF
| accessdate = 25 March
| accessyear = ]
}}</ref><ref>{{cite web
| url = http://www.atsltd.co.uk/media/papers/docs/infrastructure_cost_comparisons.doc
| title = Infrastructure cost comparisons
| format = ]
| publisher = ATS Ltd.
| accessdate = 25 March
| accessyear = 2006
}}</ref>. These estimates are considered low by sceptics, and do not account for cost overruns common in public projects. Prototype projects have reportedly been built within budget.


====Ridership attraction====
Standard transit-planning assumptions concerning overhead per vehicle are said to fail in PRT systems. These assumptions include operator salaries and transit policing. Assumptions regarding capacity utilization (the proportion of theoretical capacity which is actually utilized) are not addressed by prototype systems. The design, with many modular components, mass production, driverless operation and redundant systems, should result in low operating costs and high reliability. There are already some operational driverless transit systems. It has been observed from U.S. federal data that operations and maintenance costs (O&M) are nearly constant per seat for a wide variety of systems: buses, trains, aircraft and private automobiles. Predictions of low operating cost are predicated on weither unusually low O&M costs or increased load factor (O&M/passengers per destination). Whether this assumption is valid will not be known until full scale operations are commenced.
If PRT designs deliver the claimed benefit of being substantially faster than cars in areas with heavy traffic, simulations suggest that PRT could attract many more car drivers than other public transit systems. Standard mass transit simulations accurately predict that 2% of trips (including cars) will switch to trains. Similar methods predict that 11% to 57% of trips would switch to PRT, depending on its costs and delays.<ref name="EDICT"/><ref name=AndreassonRidership>{{cite web| last=Andreasson| first=Ingmar| title=Staged Introduction of PRT with Mass Transit| url=http://www.princeton.edu/~alaink/Orf467F10/PRT@LHR10_Conf/stagedIntroPRT_Andreasson_paper.pdf| publisher=KTH Centre for Traffic Research| access-date=2013-10-12| archive-url=https://web.archive.org/web/20131014230259/http://www.princeton.edu/~alaink/Orf467F10/PRT@LHR10_Conf/stagedIntroPRT_Andreasson_paper.pdf| archive-date=2013-10-14| url-status=dead}}</ref><ref name=YoderRidership>{{cite web| last=Yoder| title=Capital Costs and Ridership Estimates of Personal Rapid Transit| url=http://faculty.washington.edu/jbs/itrans/yoder.htm| access-date=12 October 2013|display-authors=etal}}</ref>


====Control algorithms====
The WVU PRT project failed commercially due to the cost of heating its track to eliminate snow. Some systems in which the vehicles ride atop the track therefore enclose the track to keep precipitation or debris away from the track. Snow and debris clearance is also an issue for conventional transit.
The typical control algorithm places vehicles in imaginary moving "slots" that go around the loops of track. Real vehicles are allocated a slot by track-side controllers. Traffic jams are prevented by placing north–south vehicles in even slots, and east/west vehicles in odd slots. At intersections, the traffic in these systems can interpenetrate without slowing.


On-board computers maintain their position by using a ] to stay near the center of the commanded slot. Early PRT vehicles measured their position by adding up the distance using ]s, with periodic check points to compensate for cumulative errors.<ref name="FundOfPRT" /> Next-generation ] and radio location could measure positions as well.
Conversion efficiency of electric vehicles may be in the range 40 to 90%. The typical automobile is 30% efficient; hybrid cars are 30 to 40% efficient. Smaller vehicles tend to be less efficient for a given journey than larger ones.


Another system, "pointer-following control", assigns a path and speed to a vehicle, after verifying that the path does not violate the safety margins of other vehicles. This permits system speeds and safety margins to be adjusted to design or operating conditions, and may use slightly less energy.<ref name="ControlPRT">{{cite web
Planners dispute the cost-estimates of PRT rights-of-way. In modern metropolitan areas, rights-of-way for light rail cost as much as $50 million per mile ($30 million/km). A typical light-rail right-of-way is 100 to 300 feet (30 to 100 m) wide, and necessarily includes the highest-density and most expensive parts of the operational area. Tunneling is much more expensive. PRT rights of way should cost less than a conventional road system, but the road system usually exists already.
| url = https://www.telenor.com/wp-content/uploads/2012/05/T03_1.pdf
| title = Control of Personal Rapid Transit Systems
| pages = 108–116
| publisher = Telektronikk
| date = January 2003
| access-date = August 30, 2017
}}</ref> The maker of the ULTra PRT system reports that testing of its control system shows lateral (side-to-side) accuracy of 1&nbsp;cm, and docking accuracy better than 2&nbsp;cm.


===Urban Integration=== ====Safety====
Computer control eliminates errors from human drivers, so PRT designs in a controlled environment should be much safer than private motoring on roads. Most designs enclose the running gear in the guideway to prevent derailments. Grade-separated guideways would prevent conflict with pedestrians or manually controlled vehicles. Other public transit ] approaches, such as redundancy and self-diagnosis of critical systems, are also included in designs.


The Morgantown system, more correctly described as a ] (GRT) type of ] system (AGT), has completed 110 million passenger-miles without serious injury. According to the U.S. Department of Transportation, AGT systems as a group have higher injury rates than any other form of rail-based transit (subway, metro, light rail, or commuter rail) though still much better than ordinary buses or ]s. More recent research by the British company ULTra PRT reported that AGT systems have a better safety than more conventional, non-automated modes.{{Citation needed|date=May 2008}}
In mass transit with scheduled service, this "ridership" factor is generally calculated for an entire system, then applied to all vehicles. On most trips of most routes, vehicles are 85% to 95% empty, and only rush-hour trips on important central routes approach vehicle (and route) capacities. The low ridership of bus and trains therefore often causes a substantial cash drain through depreciation and the salaries paid for operators and mechanics. Further, the drain cannot be offset by fares.


As with many current transit systems, personal passenger safety concerns are likely to be addressed through CCTV monitoring,<ref>{{cite journal |last1=Muller |first1=Peter J. |last2=Young |first2=Stanley E. |last3=Vogt |first3=Michael N. |title=Personal Rapid Transit Safety and Security on University Campus |journal=Transportation Research Record: Journal of the Transportation Research Board |date=January 2007 |volume=2006 |issue=1 |pages=95–103 |doi=10.3141/2006-11|s2cid=110883798 }}</ref> and communication with a central command center from which engineering or other assistance may be dispatched.
PRT addresses the fixed cost issues by automated fare collection, driving and only running in response to demand, or in timely expectation of demand. This idling of PRT vehicles that are in-service but not in use should save energy compared to scheduled transit modes compared to buses or trains, which move a large proportion of empty seats during non-peak periods.


====Energy efficiency====
The lower estimates of PRT designers depend on dual-use rights of way, for example by mounting the transit system on narrow poles placed on an existing street. PRT's small size can reduce the volume of its tunnel to less than a quarter of that required for an automated people mover (APM). Dual mode systems would use existing roads, as well as special-purpose PRT guideways. In some cases, the guideway is just a cable buried in the street (a technology proven in industrial automation).
The ] advantages claimed by PRT proponents include two basic operational characteristics of PRT: an increased average load factor; and the elimination of intermediate starting and stopping.<ref>{{cite web|url=http://citeseer.ist.psu.edu/594390.html|title=CiteSeerX}}</ref>


Average load factor, in transit systems, is the ratio of the total number of riders to the total theoretical capacity. A transit vehicle running at full capacity has a 100% load factor, while an empty vehicle has 0% load factor. If a transit vehicle spends half the time running at 100% and half the time running at 0%, the ''average'' load factor is 50%. Higher average load factor corresponds to lower energy consumption per passenger, so designers attempt to maximize this metric.
== Opposition and controversy ==
Opposition has been expressed to PRT schemes and their proponents based on a number of concerns:


Scheduled mass transit (i.e. buses or trains) trades off service frequency and load factor. Buses and trains must run on a predefined schedule, even during off-peak times when demand is low and vehicles are nearly empty. So to increase load factor, transportation planners try to predict times of low demand, and run reduced schedules or smaller vehicles at these times. This increases passengers' wait times. In many cities, trains and buses do not run at all at night or on weekends.
===Technical feasibility debate===
The Ohio, Kentucky, Indiana (OKI) Central Loop Report<ref>{{cite web
| url = http://www.oki.org/transportation/centralarea.html
| title = Ohio, Kentucky, Indiana (OKI) Central Loop Report
| yesr = 2001
| accessyear = 2006
}}</ref> compared the Taxi 2000 PRT concept proposed by the Skyloop Committee to other transportation modes (], ] and vintage ]). Consulting engineers with Parsons Brinckerhoff found the Taxi 2000 PRT system had "...significant environmental, technical and potential fire and life safety concerns..." and the PRT system was "...still an unproven technology with significant questions about cost and feasibility of implementation." Skyloop disputed this conclusion.


PRT vehicles, in contrast, would only move in response to demand, which places a theoretical lower bound on their average load factor. This allows 24-hour service without many of the costs of scheduled mass transit.<ref>{{citation
Vukan R. Vuchic, Professor of Transportation Engineering at the University of Pennsylvania described what he believes are problems with the PRT concept<ref>{{cite web
| author = Anderson, J. E.
| last=Vuchic
| first=Vukan R | year = 1984
| title = Optimization of Transit-System Characteristics
| publisher = Journal of Advanced Transportation, 18:1:1984, pp. 77–111
}}</ref> <!--This article may be viewed using Google's cache at:
https://scholar.google.com/scholar?hl=en&lr=&safe=off&q=cache:D7SIAd2tkzgJ:www.skywebexpress.com/pdf_files/150k_additional/OTSCpaper.pdf+PRT+%22operating+cost%22+%22demand+responsive%22
-->

ULTra PRT estimates its system will consume 839 BTU per passenger mile (0.55 ] per passenger km).<ref name="Lowson">{{cite web
| last = Lowson
| first = Martin
| url = http://www.advancedtransit.org/wp-content/uploads/2011/08/A-New-Approach-to-Sustainable-Transport-Systems-M.-Lowson.pdf
| title = A New Approach to Sustainable Transport Systems
| year = 2004
| access-date = August 30, 2017
}}</ref><ref>The conversion is: 0.55 MJ = 521.6 BTU; 1.609 km = 1 mi; therefore, 521.6 x 1.609 = 839</ref> <!-- #####I'm removing the below SkyTran section for now, because the reference link seems to be bad - I only get a page full of dead links. If that page is restored, we can restore this section. -ATren, April 2008.#####
SkyTran, a PRT concept using significantly smaller vehicles than other designs, may require only 11 horsepower (9 KW) to cruise at 160 km/h (100 mph), which translates to 151 BTU/passenger mile or 0.1 MJ per passenger km. However, SkyTran's predicted energy usage is unconfirmed in real world practice, since no SkyTran system or prototype has yet been built. Also, Skytran's small vehicle does not permit disabled passengers, which would require accommodation using other, less energy-efficient modes.<ref name="Malewicki">{{cite web
| last = Malewicki
| first = Douglas
| url = http://www.skytran.net/18EnergyEff/02Energy.htm
| title = (doc) SkyTran's Super Energy Efficiency
}} Note that this page presents a comparison of seating arrangements; the actual numbers shown for the planned 2-passenger tandem seating arrangement are 10.65 horsepower and 8.85 kilowatts. The English unit calculation is 8.85 kW / 2 passengers * 3412 (BTU/hour)/kW / 100 mile/hour = 151.0 BTU/passenger mile. The metric calculation is 8.85 kW / 2 passengers * 3.6 (MJ/hour)/kW / 160 km/hour = 0.0996 MJoule/passenger km.
</ref>--> By comparison, cars consume 3,496 BTU, and personal trucks consume 4,329 BTU per passenger mile.<ref name="edbk">{{cite web
| publisher = U.S. Dept. of Energy
| url = http://cta.ornl.gov/data/chapter2.shtml
| title = Transportation Energy Databook, 26th Edition, Ch. 2, Table 2-12
| year = 2004
}}</ref>

Due to PRT's efficiency, some proponents say solar becomes a viable power source.<ref>{{cite web
| year = 2003
| url = http://www.solarevolution.com/solutions/presentations/ATRA20061118.xls
| title = ATRA2006118: Solar PRT, p.89
| publisher = Solar Evolution
| format = Xcel Spreadsheet
| access-date = 18 November 2006
| archive-date = 30 March 2007
| archive-url = https://web.archive.org/web/20070330035545/http://www.solarevolution.com/solutions/presentations/ATRA20061118.xls
| url-status = dead
}}</ref> PRT elevated structures provide a ready platform for solar collectors, therefore some proposed designs include solar power as a characteristic of their networks.

For bus and rail transit, the energy per passenger-mile depends on the ridership and the frequency of service. Therefore, the energy per passenger-mile can vary significantly from peak to non-peak times. In the US, buses consume an average of 4,318 BTU/passenger-mile, transit rail 2,750 BTU/passenger-mile, and commuter rail 2,569 BTU/passenger-mile.<ref name="edbk"/>

==Opposition and controversy==
Opponents to PRT schemes have expressed a number of concerns:

===Technical feasibility debate===
], professor of Transportation Engineering at the ] and a proponent of traditional forms of transit, has stated his belief that the combination of small vehicles and expensive guideway makes it highly impractical in both cities (not enough capacity) and suburbs (guideway too expensive). According to Vuchic: "...the PRT concept combines two mutually incompatible elements of these two systems: very small vehicles with complicated guideways and stations. Thus, in central cities, where heavy travel volumes could justify investment in guideways, vehicles would be far too small to meet the demand. In suburbs, where small vehicles would be ideal, the extensive infrastructure would be economically unfeasible and environmentally unacceptable."<ref name="vuchic">{{cite web
| last=Vuchic | first=Vukan R
| url=http://faculty.washington.edu/jbs/itrans/vuchic1.htm | url=http://faculty.washington.edu/jbs/itrans/vuchic1.htm
| title= Personal Rapid Transit: An Unrealistic System | title= Personal Rapid Transit: An Unrealistic System
| date=September/October, 1996 | date=September–October 1996
| year=1996
| work = Urban Transport International (Paris), (No. 7, September/October, 1996) | work = Urban Transport International (Paris), (No. 7, September/October, 1996)
| access-date = 30 August 2017
| accessyear=2005
}} </ref> }}</ref>
:"The PRT concept is imagined to capture the advantages of personal service by private car with the high efficiency of rapid transit. Actually, the PRT concept combines two mutually incompatible elements of these two systems: very small vehicles with complicated guideways and stations. Thus, in central cities, where heavy travel volumes could justify investment in guideways, vehicles would be far too small to meet the demand. In suburbs, where small vehicles would be ideal, the extensive infrastructure would be economically unfeasible and environmentally unacceptable."


PRT supporters claim that Vuchic's conclusions are based on flawed assumptions. PRT proponent J.E. Anderson wrote, in a rebuttal to Vuchic: "I have studied and debated with colleagues and antagonists every objection to PRT, including those presented in papers by Professor Vuchic, and find none of substance. Among those willing to be briefed in detail and to have all of their questions and concerns answered, I find great enthusiasm to see the system built."<ref name="vuchic"/>
This has prompted an ongoing debate between Vuchic and PRT proponents.


The manufacturers of ULTra acknowledge that current forms of their system would provide insufficient capacity in high-density areas such as central ], and that the investment costs for the tracks and stations are comparable to building new roads, making the current version of ULTra more suitable for suburbs and other moderate capacity applications, or as a supplementary system in larger cities.{{citation needed|date=August 2017}}
=== Regulatory concerns ===
Possible regulatory concerns include emergency safety, headways, and accessability for the disabled. If safety or access considerations require the addition of walkways, ladders, platforms or other emergency/disabled access to or egress from PRT guideways, the size of the guideway is substantially increased. Because minimizing guideway size is important to the PRT concept and costs these concerns may be significant barriers to PRT adoption. The US and Europe both have legislation mandating disabled accessibility for public transport systems.


===Regulatory concerns===
For example, the California Public Utilities Commission states that its "Safety Rules and Regulations Governing Light Rail Transit" (General Order 143-B) and "Rules and Regulations Governing State Safety Oversight of Rail Fixed Guideway Systems" (General Order 164-C) are applicable to PRT . Both documents are available online . The degree to which CPUC would hold PRT to "light rail" and "rail fixed guideway" safety standards as a condition for safety certification is not clear.
Possible regulatory concerns include emergency safety, headways, and accessibility for the disabled. Many jurisdictions regulate PRT systems as if they were trains. At least one successful prototype, CVS, failed deployment because it could not obtain permits from regulators.<ref>See the references in ]</ref>


Several PRT systems have been proposed for ],<ref>See {{Webarchive|url=https://web.archive.org/web/20110208110916/http://santacruzprt.com/ |date=2011-02-08 }}.</ref><ref>] was proposed for ], by its inventor, Maliwicki, who lives in that area</ref> but the ] (CPUC) states that its rail regulations apply to PRT, and these require railway-sized headways.<ref name="cpuc.ca.gov">{{cite web|url=http://www.cpuc.ca.gov/PUC/documents/go.htm|title=We're so sorry, your page was Not Found!|url-status=dead|archive-url=https://web.archive.org/web/20091231144823/http://www.cpuc.ca.gov/PUC/documents/go.htm|archive-date=2009-12-31}}</ref> The degree to which CPUC would hold PRT to "light rail" and "rail fixed guideway" safety standards is not clear because it can grant particular exemptions and revise regulations.<ref>California General Order 164-D, ibid. Sections 1.3,1.4</ref>
=== Other concerns ===
Concerns have been expressed about the visual and environmental impact of (especially elevated) guideways. The 2001 OKI Report stated that Skyloop's elevated guideways and elevated stations would be visual pollution that neighborhoods would challenge in an Environmental Impact Statement (EIS). Some in the business community in Cincinnati were opposed to Skyloop's elevated guideway because it would remove potential customers from the street level.


Other forms of automated transit have been approved for use in California, notably the Airtrain system at ]. CPUC decided not to require compliance with General Order 143-B (for light rail) since Airtrain has no on-board operators. They did require compliance with General Order 164-D which mandates a safety and security plan, as well as periodic on-site visits by an oversight committee.<ref>{{cite web|url=http://docs.cpuc.ca.gov/published/Agenda_decision/22480-07.htm|title=Walker Agenda Dec - Order Concluding that Commission has Safety Jurisdiction Over SFO AirTrain}}</ref>
As with other modes of public transit, there are also concerns about policing against terrorism and vandalism, and some public transit advocates have objected to PRT promotion on the grounds that it is a distraction from other, more traditional transit solutions.


If safety or access considerations require the addition of walkways, ladders, platforms or other emergency/disabled access to or egress from PRT guideways, the size of the guideway may be increased. This may impact the feasibility of a PRT system, though the degree of impact would depend on both the PRT design and the municipality.
==References==
<references/>
=== Additional references ===
*'''', J.E. Anderson, 1978
*'''', J.E. Anderson, 2003 (PDF)
*''Systems Analysis of Urban Transportation Systems'', Scientific American, 1969, 221:19-27
*''Individualized Automated Transit in the City'', Don Fichter, 1964


===Concerns about PRT research===
==See also==
Wayne D. Cottrell of the ] conducted a critical review of PRT academic literature since the 1960s. He concluded that there are several issues that would benefit from more research, including urban integration, risks of PRT investment, bad publicity, technical problems, and competing interests from other transport modes. He suggests that these issues, "while not unsolvable, are formidable," and that the literature might be improved by better introspection and criticism of PRT. He also suggests that more government funding is essential for such research to proceed, especially in the United States.<ref>{{cite conference
* ], 1975-present
| last=Cottrell | first=Wayne D
* ] - PRT system extensively tested in the 1970s, approved by the West German government for public use.
| conference=Automated People Movers 2005: Moving to Mainstream
* ]
|title=Critical Review of the Personal Rapid Transit Literature
* ]
| publisher=ASCE
| date=May 1–4, 2005| journal = Proceedings of the 10th International Conference on Automated People Movers
| pages=1–14
| doi=10.1061/40766(174)40
| isbn=978-0-7844-0766-0
}}</ref>


===New urbanist opinion===
==External links==
Several proponents of ], an urban design movement that advocates for ], have expressed opinions on PRT.


] and ] have supported<ref> from planetizen.com</ref><ref>{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }} from planning.org</ref> the concept, but ] disagrees.<ref> {{Webarchive|url=https://web.archive.org/web/20190809194514/http://kunstlercast.com/ |date=2019-08-09 }} from kunstlercast.com</ref>


===Pilots and prototypes=== ===PRT vs. autonomous vehicles===
As the development of self-steering technology for ]s and shuttles advances,<ref>{{cite web|title=5 Companies Working On Driverless Shuttles And Buses|url=https://www.cbinsights.com/research/driverless-shuttle-companies/|publisher=CB Insights|access-date=30 August 2017|date=March 30, 2017}}</ref> the guideway technology of PRT seems obsolete at first glance. Automated operation might become feasible on existing roads too. On the other hand, PRT systems can also make use of self-steering technology and significant benefits remain from operating on a segregated route network.
* (Urban Light Transport), Cardiff Wales, UK
* , from MegaRail Transportation, Fort Worth, Texas
* , Pohang University, Korea
* , Minneapolis, Minnesota, US. 18-meter sample guideway.


===Proposals=== ==See also==
* ]
* - California & Montana, US; New Delhi, India
* ]
* - dual-mode system, but its PRT part is neccessary for viability.
* {{Annotated link|Demand responsive transport}}
* , ], Denmark
* ], a permanently discontinued personnel rapid transit system
* , a system for varying sizes of containers.
* ] (An inexpensive form of magnetic levitation.)
* - Has 385 meter test track under construction in Uppsala, Sweden.
* {{Annotated link|Parry People Movers}}
* - A Swedish concept (website and documents in Swedish)
* ]
* - Finnish version of PRT, termed "Automated Goods & People Mover" (APGM).
* ] (Human-powered PRT)
* ]
* ]
* ]


===Advocacy=== ==References==
{{Reflist|30em}}
* , The Advanced Transit Association, a professional group.
* , Citizens for Personal Rapid Transit (US)
* , Seattle, WA
* , Seattle, WA PRT news & analysis
*
* web site by Jerry Schneider.
*
*
* PRT from engineering and law point of view. Site by Oded Roth, member of Israeli Retzef team.
*
* ; Journal of Advanced Transit 34:1(2000)


==External links==
===PRT Skepticism and Criticism===
*
]
* ''Systems Analysis of Urban Transportation Systems'', Scientific American, 1969, 221:19–27
*
* —A history of PRT.
* - several Light Rail Now articles skeptical of PRT
* {{Webarchive|url=https://web.archive.org/web/20150510162253/http://ntlsearch.bts.gov/tris/record/tris/00786190.html |date=2015-05-10 }} – Book containing papers from the proceedings of the 1973 International Conference on Personal Rapid Transit (published by the University of Minnesota)
* resolution opposing public funding for PRT.
* —Website for professionals working with short distance automated transport.
* and "]en".
{{Automated trains and fixed-guideway transit}}
* ] articles.
{{Public transport}}
* by Troy Pieper
{{Emerging technologies|transport=yes}}

{{Authority control}}
] ]


] {{DEFAULTSORT:Personal Rapid Transit}}
]
]
]
]
]
]

Latest revision as of 15:25, 10 October 2024

Public transport mode
This article needs to be updated. The reason given is: There are many references throughout to what 'will', 'may', or 'should' happen when implemented; there are several PRT systems operational. Please help update this article to reflect recent events or newly available information. (February 2024)
An Ultra PRT vehicle on a test track at Heathrow Airport, London
A vehicle on West Virginia University's PRT system, Morgantown, West Virginia
Automated track-bound traffic
Automatic train operation
Lists of automated train systems
Related topics

Personal rapid transit (PRT), also referred to as podcars or guided/railed taxis, is a public transport mode featuring a network of specially built guideways on which ride small automated vehicles that carry few (generally less than 6) passengers per vehicle. PRT is a type of automated guideway transit (AGT), a class of system which also includes larger vehicles all the way to small subway systems. In terms of routing, it tends towards personal public transport systems.

PRT vehicles are sized for individual or small group travel, typically carrying no more than three to six passengers per vehicle. Guideways are arranged in a network topology, with all stations located on sidings, and with frequent merge/diverge points. This allows for nonstop, point-to-point travel, bypassing all intermediate stations. The point-to-point service has been compared to a taxi or a horizontal lift (elevator).

Numerous PRT systems have been proposed but most have not been implemented. As of November 2016, only a handful of PRT systems are operational: Morgantown Personal Rapid Transit (the oldest and most extensive), in Morgantown, West Virginia, has been in continuous operation since 1975. Since 2010 a 10-vehicle 2getthere system has operated at Masdar City, UAE, and since 2011 a 21-vehicle Ultra PRT system has run at London Heathrow Airport. A 40-vehicle Vectus system with in-line stations officially opened in Suncheon, South Korea, in April 2014. A PRT system connecting the terminals and parking has been built at the new Chengdu Tianfu International Airport, which opened in 2021.

Overview

Most mass transit systems move people in groups over scheduled routes. This has inherent inefficiencies. For passengers, time is wasted by waiting for the next vehicle to arrive, indirect routes to their destination, stopping for passengers with other destinations, and often confusing or inconsistent schedules. Slowing and accelerating large weights can undermine public transport's benefit to the environment while slowing other traffic.

Personal rapid transit systems attempt to eliminate these wastes by moving small groups nonstop in automated vehicles on fixed tracks. Passengers can ideally board a pod immediately upon arriving at a station, and can – with a sufficiently extensive network of tracks – take relatively direct routes to their destination without stops.

The low weight of PRT's small vehicles allows smaller guideways and support structures than mass transit systems like light rail. The smaller structures translate into lower construction costs, smaller easements, and less visually obtrusive infrastructure.

As it stands, a citywide deployment with many lines and closely spaced stations, as envisioned by proponents, has yet to be constructed. Past projects have failed because of financing, cost overruns, regulatory conflicts, political issues, misapplied technology, and flaws in design, engineering or review.

However, the theory remains active. For example, from 2002 to 2005, the EDICT project, sponsored by the European Union, conducted a study on the feasibility of PRT in four European cities. The study involved 12 research organizations, and concluded that PRT:

  • would provide future cities "a highly accessible, user-responsive, environmentally friendly transport system which offers a sustainable and economic solution."
  • could "cover its operating costs, and provide a return which could pay for most, if not all, of its capital costs."
  • would provide "a level of service which is superior to that available from conventional public transport."
  • would be "well received by the public, both public transport and car users."

The report also concluded that, despite these advantages, public authorities will not commit to building PRT because of the risks associated with being the first public implementation.

Comparison of personal rapid transit with existing transport systems
Similar to cars / automobiles
  • Vehicles are small—typically two to six passengers
  • Vehicles are individually hired, like taxis, and shared only with the passengers of one's choosing
  • Vehicles travel along a network of guideways, much like a network of streets. Travel is point-to-point, with no intermediate stops or transfers
  • Potential for on-demand, around-the-clock availability
  • Stops are designed to be off the main guideway, allowing through traffic to bypass stations unimpeded
Similar to trams, buses, and monorails
  • A public amenity (although not necessarily publicly owned), shared by multiple users
  • Reduced local pollution (electric powered)
  • Passengers embark and disembark at discrete stations, analogous to bus stops or taxi stands
Similar to automated people movers
  • Fully automated, including vehicle control, routing, and collection of fares
  • Usually above the street—typically elevated—reducing land usage and congestion
Distinct features
  • Vehicle movements may be coordinated, unlike the autonomous human control of cars and bikes
  • Small vehicle size allows infrastructure to be smaller than other transit modes
  • Automated vehicles can travel close together. Possibilities include dynamically combined "trains" of vehicles, separated by a few inches, to reduce drag and increase speed, energy efficiency and passenger density

The PRT acronym was introduced formally in 1978 by J. Edward Anderson. The Advanced Transit Association (ATRA), a group which advocates the use of technological solutions to transit problems, compiled a definition in 1988 that can be seen here.

List of operational automated transit networks (ATN) systems

Currently, five advanced transit networks (ATN) systems are operational, and several more are in the planning stage.

System Manufacturer Type Locations Length Stations / vehicles Notes
Morgantown PRT Boeing GRT

United States Morgantown, West Virginia, US (1975)

13.2 km (8.2 mi) 5 / 73 Up to 20 passengers per vehicle, some rides not point-to-point during low usage periods
ParkShuttle 2getthere GRT Netherlands Rivium, the Netherlands (November 2005) 1.8 km (1.1 mi) 5 2nd generation GRT (Group Rapid Transit) vehicles accommodate up to 24 passengers (12 seated). The vehicles operate on-schedule during peak hours, at a 2.5 minute interval, and can operate on demand during off-peak hours. The current system will operate until the end of 2018, after which it is expected to be replaced and expanded.
CyberCab 2getthere PRT United Arab Emirates Masdar City, Abu Dhabi, UAE (November 2010) 1.5 km (0.9 mi) 2/10 passenger, (3/3 freight, not put into service) Initial plans called for cars to be banned, with PRT as the only powered intra-city transport (along with an inter-city light rail line). In October 2010 it was announced the PRT would not expand beyond the pilot scheme due to the cost of creating the undercroft to segregate the system from pedestrian traffic. Plans now include electric cars and electric buses. In June 2013 a representative of the builder 2getthere said the freight vehicles had still not been put into service because they had not worked out how to get freight to and from the stations.
Ultra PRT Heathrow pod PRT United Kingdom Heathrow Airport, England, UK (June 2011) 3.8 km (2.4 mi) 3 / 21 The Heathrow PRT system became operational in 2011, connecting Terminal 5 with a long-term car park. In May 2014 BAA said in a draft 5-year plan that it would extend the system throughout the airport, but this was dropped from the final plan.
Skycube Vectus PRT South Korea Suncheon, South Korea (September 2013) 4.64 km (2.9 mi) 2 / 40 Connects the site of 2013 Suncheon Garden Expo Korea to a station in the wetlands "Buffer Area" next to the Suncheon Literature Museum; the line runs parallel to the Suncheon-dong Stream. Stations are "on-line."
Ultra PRT Kunming Shipbuilding Equipment PRT China Tianfu Airport, Chengdu, China 5 km (3.1 miles) 3 / 22

List of ATN suppliers

Main article: List of automated transit networks suppliers

The following list summarizes several well-known automated transit networks (ATN) suppliers as of 2014, with subsequent amendments.

History

Origins

Modern PRT concepts began around 1953 when Donn Fichter, a city transportation planner, began research on PRT and alternative transportation methods. In 1964, Fichter published a book which proposed an automated public transit system for areas of medium to low population density. One of the key points made in the book was Fichter's belief that people would not leave their cars in favor of public transit unless the system offered flexibility and end-to-end transit times that were much better than existing systems – flexibility and performance he felt only a PRT system could provide. Several other urban and transit planners also wrote on the topic and some early experimentation followed, but PRT remained relatively unknown.

Around the same time, Edward Haltom was studying monorail systems. Haltom noticed that the time to start and stop a conventional large monorail train, like those of the Wuppertal Schwebebahn, meant that a single line could only support between 20 and 40 vehicles an hour. In order to get reasonable passenger movements on such a system, the trains had to be large enough to carry hundreds of passengers (see headway for a general discussion). This, in turn, demanded large guideways that could support the weight of these large vehicles, driving up capital costs to the point where he considered them unattractive.

Haltom turned his attention to developing a system that could operate with shorter timings, thereby allowing the individual cars to be smaller while preserving the same overall route capacity. Smaller cars would mean less weight at any given point, which meant smaller and less expensive guideways. To eliminate the backup at stations, the system used "offline" stations that allowed the mainline traffic to bypass the stopped vehicles. He designed the Monocab system using six-passenger cars suspended on wheels from an overhead guideway. Like most suspended systems, it suffered from the problem of difficult switching arrangements. Since the car rode on a rail, switching from one path to another required the rail to be moved, a slow process that limited the possible headways.

UMTA is formed

By the late 1950s the problems with urban sprawl were becoming evident in the United States. When cities improved roads and the transit times were lowered, suburbs developed at ever increasing distances from the city cores, and people moved out of the downtown areas. Lacking pollution control systems, the rapid rise in car ownership and the longer trips to and from work were causing significant air quality problems. Additionally, movement to the suburbs led to a flight of capital from the downtown areas, one cause of the rapid urban decay seen in the US.

Mass transit systems were one way to combat these problems. Yet during this period, the federal government was feeding the problems by funding the development of the Interstate Highway System, while at the same time funding for mass transit was being rapidly scaled back. Public transit ridership in most cities plummeted.

In 1962, President John F. Kennedy charged Congress with the task of addressing these problems. These plans came to fruition in 1964, when President Lyndon B. Johnson signed the Urban Mass Transportation Act of 1964 into law, thereby forming the Urban Mass Transportation Administration. UMTA was set up to fund mass transit developments in the same fashion that the earlier Federal Aid Highway Act of 1956 had helped create the Interstate Highways. That is, UMTA would help cover the capital costs of building out new infrastructure.

PRT research starts

However, planners who were aware of the PRT concept were worried that building more systems based on existing technologies would not help the problem, as Fitcher had earlier noted. Proponents suggested that systems would have to offer the flexibility of a car:

The reason for the sad state of public transit is a very basic one – the transit systems just do not offer a service which will attract people away from their automobiles. Consequently, their patronage comes very largely from those who cannot drive, either because they are too young, too old, or because they are too poor to own and operate an automobile. Look at it from the standpoint of a commuter who lives in a suburb and is trying to get to work in the central business district (CBD). If he is going to go by transit, a typical scenario might be the following: he must first walk to the closest bus stop, let us say a five or ten minute walk, and then he may have to wait up to another ten minutes, possibly in inclement weather, for the bus to arrive. When it arrives, he may have to stand unless he is lucky enough to find a seat. The bus will be caught up in street congestion and move slowly, and it will make many stops completely unrelated to his trip objective. The bus may then let him off at a terminal to a suburban train. Again he must wait, and, after boarding the train, again experience a number of stops on the way to the CBD, and possibly again he may have to stand in the aisle. He will get off at the station most convenient to his destination and possibly have to transfer again onto a distribution system. It is no wonder that in those cities where ample inexpensive parking is available, most of those who can drive do drive.

In 1966, the United States Department of Housing and Urban Development was asked to "undertake a project to study ... new systems of urban transportation that will carry people and goods ... speedily, safely, without polluting the air, and in a manner that will contribute to sound city planning." The resulting report was published in 1968 and proposed the development of PRT, as well as other systems such as dial-a-bus and high-speed interurban links.

In the late 1960s, the Aerospace Corporation, an independent non-profit corporation set up by the US Congress, spent substantial time and money on PRT, and performed much of the early theoretical and systems analysis. However, this corporation is not allowed to sell to non-federal government customers. In 1969, members of the study team published the first widely publicized description of PRT in Scientific American. In 1978 the team also published a book. These publications sparked off a sort of "transit race" in the same sort of fashion as the space race, with countries around the world rushing to join what appeared to be a future market of immense size.

The oil crisis of 1973 made vehicle fuels more expensive, which naturally interested people in alternative transportation.

System developments

In 1967, aerospace giant Matra started the Aramis project in Paris. After spending about 500 million francs, the project was canceled when it failed its qualification trials in November 1987. The designers tried to make Aramis work like a "virtual train", but control software issues caused cars to bump unacceptably. The project ultimately failed.

Between 1970 and 1978, Japan operated a project called "Computer-controlled Vehicle System" (CVS). In a full-scale test facility, 84 vehicles operated at speeds up to 60 kilometres per hour (37.3 mph) on a 4.8 km (3.0 mi) guideway; one-second headways were achieved during tests. Another version of CVS was in public operation for six months from 1975 to 1976. This system had 12 single-mode vehicles and four dual-mode vehicles on a 1.6 km (1.0 mi) track with five stations. This version carried over 800,000 passengers. CVS was cancelled when Japan's Ministry of Land, Infrastructure and Transport declared it unsafe under existing rail safety regulations, specifically in respect of braking and headway distances.

On March 23, 1973, U.S. Urban Mass Transportation Administration (UMTA) administrator Frank Herringer testified before Congress: "A DOT program leading to the development of a short, one-half to one-second headway, high-capacity PRT (HCPRT) system will be initiated in fiscal year 1974." According to PRT supporter J. Edward Anderson, this was "because of heavy lobbying from interests fearful of becoming irrelevant if a genuine PRT program became visible." From that time forward people interested in HCPRT were unable to obtain UMTA research funding.

In 1975, the Morgantown Personal Rapid Transit project was completed. It has five off-line stations that enable non-stop, individually programmed trips along an 8.7-mile (14.0 km) track serviced by a fleet of 71 cars. This is a crucial characteristic of PRT. However, it is not considered a PRT system because its vehicles are too heavy and carry too many people. When it carries many people, it operates in a point-to-point fashion, instead of running like an automated people mover from one end of the line to the other. During periods of low usage all cars make a full circuit stopping at every station in both directions. Morgantown PRT is still in continuous operation at West Virginia University in Morgantown, West Virginia, with about 15,000 riders per day (as of 2003). The steam-heated track has proven expensive and the system requires an operation and maintenance budget of $5 million annually. Although it successfully demonstrated automated control and it is still operating it was not sold to other sites. A 2010 report concluded replacing the system with buses on roads would provide unsatisfactory service and create congestion. Subsequently, the forty year old computer and vehicle control systems were replaced in the 2010s and there are plans to replace the vehicles.

From 1969 to 1980, Mannesmann Demag and MBB cooperated to build the Cabinentaxi urban transportation system in Germany. Together the firms formed the Cabintaxi Joint Venture. They created an extensive PRT technology, including a test track, that was considered fully developed by the German government and its safety authorities. The system was to have been installed in Hamburg, but budget cuts stopped the proposed project before the start of construction. With no other potential projects on the horizon, the joint venture disbanded, and the fully developed PRT technology was never installed. Cabintaxi Corporation, a US-based company, obtained the technology in 1985, and remains active in the private-sector market trying to sell the system but so far there have been no installations.

In 1979 the three station Duke University Medical Center Patient Rapid Transit system was commissioned. Uniquely, the cars could move sideways, as well as backwards and forwards and it was described as a "horizontal elevator". The system was closed in 2009 to allow for expansion of the hospital.

In the 1990s, Raytheon invested heavily in a system called PRT 2000, based on technology developed by J. Edward Anderson at the University of Minnesota. Raytheon failed to install a contracted system in Rosemont, Illinois, near Chicago, when estimated costs escalated to US$50 million per mile, allegedly due to design changes that increased the weight and cost of the system relative to Anderson's original design. In 2000, rights to the technology reverted to the University of Minnesota, and were subsequently purchased by Taxi2000.

Later developments

In 1999 the 2getthere designed ParkShuttle system was opened in the Kralingen neighbourhood of eastern Rotterdam using 12-seater driverless buses. The system was extended in 2005 and new second-generation vehicles introduced to serve five stations over 1.8 kilometres (1.1 mi) with five grade crossings over ordinary roads. Operation is scheduled in peak periods and on demand at other times. In 2002, 2getthere operated twenty five 4-passenger "CyberCabs" at Holland's 2002 Floriade horticultural exhibition. These transported passengers along a track spiraling up to the summit of Big Spotters Hill. The track was approximately 600-metre (1,969 ft) long (one-way) and featured only two stations. The six-month operation was intended to research the public acceptance of PRT-like systems.

In 2010 a 10-vehicle (four seats each), two station 2getthere system was opened to connect a parking lot to the main area at Masdar City, UAE. The systems runs in an undercroft beneath the city and was supposed to be a pilot project for a much larger network, which would also have included transport of freight. Expansion of the system was cancelled just after the pilot scheme opened due to the cost of constructing the undercroft and since then other electric vehicles have been proposed.

In January 2003, the prototype ULTra ("Urban Light Transport") system in Cardiff, Wales, was certified to carry passengers by the UK Railway Inspectorate on a 1 km (0.6 mi) test track. ULTra was selected in October 2005 by BAA plc for London's Heathrow Airport. Since May 2011 a three-station system has been open to the public, transporting passengers from a remote parking lot to terminal 5. During the deployment of the system the owners of Heathrow became owners of the UltrPRT design. In May 2013 Heathrow Airport Limited included in its draft five-year (2014–2019) master plan a scheme to use the PRT system to connect terminal 2 and terminal 3 to their respective business car parks. The proposal was not included in the final plan due to spending priority given to other capital projects and has been deferred. If a third runway is constructed at Heathrow will destroy the existing system, which will be built over, will be replaced by another PRT.

In June 2006, a Korean/Swedish consortium, Vectus Ltd, started constructing a 400 m (1,312 ft) test track in Uppsala, Sweden. This test system was presented at the 2007 PodCar City conference in Uppsala. A 40-vehicle, 2-station, 4.46 km (2.8 mi) system called "SkyCube" was opened in Suncheon, South Korea, in April 2014.

In the 2010s the Mexican Western Institute of Technology and Higher Education began research into project LINT ("Lean Intelligent Network Transportation") and built a 1/12 operational scale model. This was further developed and became the Modutram system and a full-scale test track was built in Guadalajara, which was operational by 2014.

In 2018 it was announced that a PRT system would be installed at the new Chengdu Tianfu International Airport. The system will include 6 miles of guideway, 4 stations, 22 pods and will connect airport parking to two terminal buildings. It is supplied by Ultra MTS. The airport is due to open in 2021.

System design

Among the handful of prototype systems (and the larger number that exist on paper) there is a substantial diversity of design approaches, some of which are controversial.

Vehicle design

Vehicle weight influences the size and cost of a system's guideways, which are in turn a major part of the capital cost of the system. Larger vehicles are more expensive to produce, require larger and more expensive guideways, and use more energy to start and stop. If vehicles are too large, point-to-point routing also becomes more expensive. Against this, smaller vehicles have more surface area per passenger (thus have higher total air resistance which dominates the energy cost of keeping vehicles moving at speed), and larger motors are generally more efficient than smaller ones.

The number of riders who will share a vehicle is a key unknown. In the U.S., the average car carries 1.16 persons, and most industrialized countries commonly average below two people; not having to share a vehicle with strangers is a key advantage of private transport. Based on these figures, some have suggested that two passengers per vehicle (such as with skyTran, EcoPRT and Glydways), or even a single passenger per vehicle is optimum. Other designs use a car for a model, and choose larger vehicles, making it possible to accommodate families with small children, riders with bicycles, disabled passengers with wheelchairs, or a pallet or two of freight.

Propulsion

All current designs (except for the human-powered Shweeb) are powered by electricity. In order to reduce vehicle weight, power is generally transmitted via lineside conductors although two of the operating systems use on-board batteries. According to the designer of Skyweb/Taxi2000, J. Edward Anderson, the lightest system uses linear induction motor (LIM) on the vehicle for both propulsion and braking, which also makes manoeuvres consistent regardless of the weather, especially rain or snow. LIMs are used in a small number of rapid transit applications, but most designs use rotary motors. Most such systems retain a small on-board battery to reach the next stop after a power failure. CabinTaxi uses a LIM and was able to demonstrate 0.5 second headways on its test track. The Vectus prototype system used continuous track mounted LIMs with the reaction plate on the vehicle, eliminating the active propulsion system (and power required) on the vehicle.

ULTra and 2getthere use on-board batteries, recharged at stations. This increases the safety, and reduces the complexity, cost and maintenance of the guideway. As a result, the ULTRa guideway resembles a sidewalk with curbs and is inexpensive to construct. ULTRa and 2getthere vehicles resembles small automated electric cars, and use similar components. (The ULTRa POD chassis and cabin have been used as the basis of a shared autonomous vehicle for running in mixed traffic.)

Switching

Almost all designs avoid track switching, instead advocating vehicle-mounted switches (which engage with special guiderails at the junctions) or conventional steering. Advocates say that vehicle-switching permits faster routing so vehicles can run closer together which increases capacity. It also simplifies the guideway, makes junctions less visually obtrusive and reduces the impact of malfunctions, because a failed switch on one vehicle is less likely to affect other vehicles.

Track switching greatly increases headway distance. A vehicle must wait for the previous vehicle to clear the junction, for the track to switch and for the switch to be verified. Communication between the vehicle and wayside controllers adds both delays and more points of failure. If the track switching is faulty, vehicles must be able to stop before reaching the switch, and all vehicles approaching the failed junction would be affected.

Mechanical vehicle switching minimizes inter-vehicle spacing or headway distance, but it also increases the minimum distances between consecutive junctions. A mechanically switching vehicle, maneuvering between two adjacent junctions with different switch settings, cannot proceed from one junction to the next. The vehicle must adopt a new switch position, and then wait for the in-vehicle switch's locking mechanism to be verified. If the vehicle switching is faulty, that vehicle must be able to stop before reaching the next switch, and all vehicles approaching the failed vehicle would be affected.

Conventional steering allows a simpler 'track' consisting only of a road surface with some form of reference for the vehicle's steering sensors. Switching would be accomplished by the vehicle following the appropriate reference line – maintaining a set distance from the left roadway edge would cause the vehicle to diverge left at a junction, for example.

Infrastructure design

Simplified depiction of a possible PRT network. The blue rectangles indicate stations. The enlarged portion illustrates a station off-ramp.

Guideways

Several types of guideways have been proposed or implemented, including beams similar to monorails, bridge-like trusses supporting internal tracks, and cables embedded in a roadway. Most designs put the vehicle on top of the track, which reduces visual intrusion and cost, as well as easing ground-level installation. An overhead track is necessarily higher, but may also be narrower. Most designs use the guideway to distribute power and data communications, including to the vehicles. The Morgantown PRT failed its cost targets because of the steam-heated track required to keep the large channel guideway free of frequent snow and ice. Heating uses up to four times as much as energy as that used to propel the vehicles. Most proposals plan to resist snow and ice in ways that should be less expensive. The Heathrow system has a special de-icing vehicle. Masdar's system has been limited because the exclusive right-of-way for the PRT was gained by running the vehicles in an undercroft at ground-level while building an elevated "street level" between all the buildings. This led to unrealistically expensive buildings and roads.

Stations

Proposals usually have stations close together, and located on side tracks so that through traffic can bypass vehicles picking up or dropping off passengers. Each station might have multiple berths, with perhaps one-third of the vehicles in a system being stored at stations waiting for passengers. Stations are envisioned to be minimalistic, without facilities such as rest rooms. For elevated stations, an elevator may be required for accessibility.

At least one system, Metrino, provides wheelchair and freight access by using a cogway in the track, so that the vehicle itself can go from a street-level stop to an overhead track.

Some designs have included substantial extra expense for the track needed to decelerate to and accelerate from stations. In at least one system, Aramis, this nearly doubled the width and cost of the required right-of-way and caused the nonstop passenger delivery concept to be abandoned. Other designs have schemes to reduce this cost, for example merging vertically to reduce the footprint.

Operational characteristics

Headway distance

Spacing of vehicles on the guideway influences the maximum passenger capacity of a track, so designers prefer smaller headway distances. Computerized control and active electronic braking (of motors) theoretically permit much closer spacing than the two-second headways recommended for cars at speed. In these arrangements, multiple vehicles operate in "platoons" and can be braked simultaneously. There are prototypes for automatic guidance of private cars based on similar principles.

Very short headways are controversial. The UK Railway Inspectorate has evaluated the ULTra design and is willing to accept one-second headways, pending successful completion of initial operational tests at more than 2 seconds. In other jurisdictions, preexisting rail regulations apply to PRT systems (see CVS, above); these typically calculate headways for absolute stopping distances with standing passengers. These severely restrict capacity and make PRT systems infeasible. Another standard said trailing vehicles must stop if the vehicle in front stopped instantaneously (or like a "brick wall"). In 2018 a committee of the American Society of Mechanical Engineers considered replacing the "brick wall" standard with a requirement for vehicles to maintain a safe "separation zone" based on the minimum stopping distance of the lead vehicle and the maximum stopping of the trailing vehicle. These changes were introduced into the standard in 2021.

Capacity

PRT is usually proposed as an alternative to rail systems, so comparisons tend to be with rail. PRT vehicles seat fewer passengers than trains and buses, and must offset this by combining higher average speeds, diverse routes, and shorter headways. Proponents assert that equivalent or higher overall capacity can be achieved by these means.

Single line capacity

With two-second headways and four-person vehicles, a single PRT line can achieve theoretical maximum capacity of 7,200 passengers per hour. However, most estimates assume that vehicles will not generally be filled to capacity, due to the point-to-point nature of PRT. At a more typical average vehicle occupancy of 1.5 persons per vehicle, the maximum capacity is 2,700 passengers per hour. Some researchers have suggested that rush hour capacity can be improved if operating policies support ridesharing.

Capacity is inversely proportional to headway. Therefore, moving from two-second headways to one-second headways would double PRT capacity. Half-second headways would quadruple capacity. Theoretical minimum PRT headways would be based on the mechanical time to engage brakes, and these are much less than a half second. Researchers suggest that high capacity PRT (HCPRT) designs could operate safely at half-second headways, which has already been achieved in practice on the Cabintaxi test track in the late 1970s. Using the above figures, capacities above 10,000 passengers per hour seem in reach.

In simulations of rush hour or high-traffic events, about one-third of vehicles on the guideway need to travel empty to resupply stations with vehicles in order to minimize response time. This is analogous to trains and buses travelling nearly empty on the return trip to pick up more rush hour passengers.

Grade separated light rail systems can move 15,000 passengers per hour on a fixed route, but these are usually fully grade separated systems. Street level systems typically move up to 7,500 passengers per hour. Heavy rail subways can move 50,000 passengers per hour per direction. As with PRT, these estimates depend on having enough trains.

Neither light nor heavy rail scales operated efficiently in off-peak when capacity utilization is low but a schedule must be maintained. In a PRT system when demand is low, surplus vehicles will be configured to stop at empty stations at strategically placed points around the network. This enables an empty vehicle to quickly be despatched to wherever it is required, with minimal waiting time for the passenger. PRT systems will have to re-circulate empty vehicles if there is an imbalance in demand along a route, as is common in peak periods.

Networked PRT capacity

The above discussion compares line or corridor capacity and may therefore not be relevant for a networked PRT system, where several parallel lines (or parallel components of a grid) carry traffic. In addition, Muller estimated that while PRT may need more than one guideway to match the capacity of a conventional system, the capital cost of the multiple guideways may still be less than that of the single guideway conventional system. Thus comparisons of line capacity should also consider the cost per line.

PRT systems should require much less horizontal space than existing metro systems, with individual cars being typically around 50% as wide for side-by-side seating configurations, and less than 33% as wide for single-file configurations. This is an important factor in densely populated, high-traffic areas.

Travel speed

For a given peak speed, nonstop journeys are about three times as fast as those with intermediate stops. This is not just because of the time for starting and stopping. Scheduled vehicles are also slowed by boardings and exits for multiple destinations.

Therefore, a given PRT seat transports about three times as many passenger miles per day as a seat performing scheduled stops. So PRT should also reduce the number of needed seats threefold for a given number of passenger miles.

While a few PRT designs have operating speeds of 100 km/h (62 mph), and one as high as 241 km/h (150 mph), most are in the region of 40–70 km/h (25–43 mph). Rail systems generally have higher maximum speeds, typically 90–130 km/h (56–81 mph) and sometimes well in excess of 160 km/h (99 mph), but average travel speed is reduced about threefold by scheduled stops and passenger transfers.

Ridership attraction

If PRT designs deliver the claimed benefit of being substantially faster than cars in areas with heavy traffic, simulations suggest that PRT could attract many more car drivers than other public transit systems. Standard mass transit simulations accurately predict that 2% of trips (including cars) will switch to trains. Similar methods predict that 11% to 57% of trips would switch to PRT, depending on its costs and delays.

Control algorithms

The typical control algorithm places vehicles in imaginary moving "slots" that go around the loops of track. Real vehicles are allocated a slot by track-side controllers. Traffic jams are prevented by placing north–south vehicles in even slots, and east/west vehicles in odd slots. At intersections, the traffic in these systems can interpenetrate without slowing.

On-board computers maintain their position by using a negative feedback loop to stay near the center of the commanded slot. Early PRT vehicles measured their position by adding up the distance using odometers, with periodic check points to compensate for cumulative errors. Next-generation GPS and radio location could measure positions as well.

Another system, "pointer-following control", assigns a path and speed to a vehicle, after verifying that the path does not violate the safety margins of other vehicles. This permits system speeds and safety margins to be adjusted to design or operating conditions, and may use slightly less energy. The maker of the ULTra PRT system reports that testing of its control system shows lateral (side-to-side) accuracy of 1 cm, and docking accuracy better than 2 cm.

Safety

Computer control eliminates errors from human drivers, so PRT designs in a controlled environment should be much safer than private motoring on roads. Most designs enclose the running gear in the guideway to prevent derailments. Grade-separated guideways would prevent conflict with pedestrians or manually controlled vehicles. Other public transit safety engineering approaches, such as redundancy and self-diagnosis of critical systems, are also included in designs.

The Morgantown system, more correctly described as a Group Rapid Transit (GRT) type of Automated Guideway Transit system (AGT), has completed 110 million passenger-miles without serious injury. According to the U.S. Department of Transportation, AGT systems as a group have higher injury rates than any other form of rail-based transit (subway, metro, light rail, or commuter rail) though still much better than ordinary buses or cars. More recent research by the British company ULTra PRT reported that AGT systems have a better safety than more conventional, non-automated modes.

As with many current transit systems, personal passenger safety concerns are likely to be addressed through CCTV monitoring, and communication with a central command center from which engineering or other assistance may be dispatched.

Energy efficiency

The energy efficiency advantages claimed by PRT proponents include two basic operational characteristics of PRT: an increased average load factor; and the elimination of intermediate starting and stopping.

Average load factor, in transit systems, is the ratio of the total number of riders to the total theoretical capacity. A transit vehicle running at full capacity has a 100% load factor, while an empty vehicle has 0% load factor. If a transit vehicle spends half the time running at 100% and half the time running at 0%, the average load factor is 50%. Higher average load factor corresponds to lower energy consumption per passenger, so designers attempt to maximize this metric.

Scheduled mass transit (i.e. buses or trains) trades off service frequency and load factor. Buses and trains must run on a predefined schedule, even during off-peak times when demand is low and vehicles are nearly empty. So to increase load factor, transportation planners try to predict times of low demand, and run reduced schedules or smaller vehicles at these times. This increases passengers' wait times. In many cities, trains and buses do not run at all at night or on weekends.

PRT vehicles, in contrast, would only move in response to demand, which places a theoretical lower bound on their average load factor. This allows 24-hour service without many of the costs of scheduled mass transit.

ULTra PRT estimates its system will consume 839 BTU per passenger mile (0.55 MJ per passenger km). By comparison, cars consume 3,496 BTU, and personal trucks consume 4,329 BTU per passenger mile.

Due to PRT's efficiency, some proponents say solar becomes a viable power source. PRT elevated structures provide a ready platform for solar collectors, therefore some proposed designs include solar power as a characteristic of their networks.

For bus and rail transit, the energy per passenger-mile depends on the ridership and the frequency of service. Therefore, the energy per passenger-mile can vary significantly from peak to non-peak times. In the US, buses consume an average of 4,318 BTU/passenger-mile, transit rail 2,750 BTU/passenger-mile, and commuter rail 2,569 BTU/passenger-mile.

Opposition and controversy

Opponents to PRT schemes have expressed a number of concerns:

Technical feasibility debate

Vukan R. Vuchic, professor of Transportation Engineering at the University of Pennsylvania and a proponent of traditional forms of transit, has stated his belief that the combination of small vehicles and expensive guideway makes it highly impractical in both cities (not enough capacity) and suburbs (guideway too expensive). According to Vuchic: "...the PRT concept combines two mutually incompatible elements of these two systems: very small vehicles with complicated guideways and stations. Thus, in central cities, where heavy travel volumes could justify investment in guideways, vehicles would be far too small to meet the demand. In suburbs, where small vehicles would be ideal, the extensive infrastructure would be economically unfeasible and environmentally unacceptable."

PRT supporters claim that Vuchic's conclusions are based on flawed assumptions. PRT proponent J.E. Anderson wrote, in a rebuttal to Vuchic: "I have studied and debated with colleagues and antagonists every objection to PRT, including those presented in papers by Professor Vuchic, and find none of substance. Among those willing to be briefed in detail and to have all of their questions and concerns answered, I find great enthusiasm to see the system built."

The manufacturers of ULTra acknowledge that current forms of their system would provide insufficient capacity in high-density areas such as central London, and that the investment costs for the tracks and stations are comparable to building new roads, making the current version of ULTra more suitable for suburbs and other moderate capacity applications, or as a supplementary system in larger cities.

Regulatory concerns

Possible regulatory concerns include emergency safety, headways, and accessibility for the disabled. Many jurisdictions regulate PRT systems as if they were trains. At least one successful prototype, CVS, failed deployment because it could not obtain permits from regulators.

Several PRT systems have been proposed for California, but the California Public Utilities Commission (CPUC) states that its rail regulations apply to PRT, and these require railway-sized headways. The degree to which CPUC would hold PRT to "light rail" and "rail fixed guideway" safety standards is not clear because it can grant particular exemptions and revise regulations.

Other forms of automated transit have been approved for use in California, notably the Airtrain system at SFO. CPUC decided not to require compliance with General Order 143-B (for light rail) since Airtrain has no on-board operators. They did require compliance with General Order 164-D which mandates a safety and security plan, as well as periodic on-site visits by an oversight committee.

If safety or access considerations require the addition of walkways, ladders, platforms or other emergency/disabled access to or egress from PRT guideways, the size of the guideway may be increased. This may impact the feasibility of a PRT system, though the degree of impact would depend on both the PRT design and the municipality.

Concerns about PRT research

Wayne D. Cottrell of the University of Utah conducted a critical review of PRT academic literature since the 1960s. He concluded that there are several issues that would benefit from more research, including urban integration, risks of PRT investment, bad publicity, technical problems, and competing interests from other transport modes. He suggests that these issues, "while not unsolvable, are formidable," and that the literature might be improved by better introspection and criticism of PRT. He also suggests that more government funding is essential for such research to proceed, especially in the United States.

New urbanist opinion

Several proponents of new urbanism, an urban design movement that advocates for walkable cities, have expressed opinions on PRT.

Peter Calthorpe and Sir Peter Hall have supported the concept, but James Howard Kunstler disagrees.

PRT vs. autonomous vehicles

As the development of self-steering technology for autonomous cars and shuttles advances, the guideway technology of PRT seems obsolete at first glance. Automated operation might become feasible on existing roads too. On the other hand, PRT systems can also make use of self-steering technology and significant benefits remain from operating on a segregated route network.

See also

References

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