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For the use of "unimodal" in mathematics and statistics, see Unimodal function

UniModal or SkyTran is a proposal by Douglas Malewicki for a 160km/h (100mph) personal rapid transit system using passive magnetic levitation and electric linear propulsion. For the current status of SkyTran, look here.

Introduction

Each automated pod (the vehicle that carries passengers or cargo) would be suspended from a magnetically-levitated overhead guideway. The magnetic levitation system would be the passive "Inductrack" system using Halbach arrays, as developed by physicist Richard Post at Lawrence Livermore Laboratories.

Most PRT systems are just "cars on elevated tracks" and therefore inherit inefficiencies similar to conventional cars. However, the UniModal system is designed to transport people with greater speed, lower cost, and better comfort, safety and convenience than an automobile or bus, or most PRT systems.

All PRT systems offer nonstop point-to-point travel without waiting. Unimodal's high speeds are said to increase its convenience and attraction for users. The speed would reduce the greatest wasted value of most transit systems: passenger time.

The high speeds permit a Unimodal car to have many trips per hour, increasing passenger capacity and reducing the fleet size needed during rush-hour. Having smaller fleet size would reduce all the costs and space associated with it, including public costs such as storage of vehicles.

System Description

Hypothetical Trip

A person would approach a portal (a stair-structure where pods stop), walk up the stairs, and get in the ready pod. One would tell (verbally) the pod where they want to go, and the pod door would close automatically. The pod would then accelerate forward and up along the acceleration guideway, and would then merge with the main guideway at 100 mph. The pod would travel to the destination portal and would exit on the decelerate track, then start slowing down, and presently stop at an exit portal. The door would automatically open, and the person would get out and walk down the stairs. The pod would then close its door, and edge forward to wait in a line with other pods, all waiting for people to use the pod in front at the entrance portal.

Ideal Guideway Grid

The guideway is designed to accommodate a 3D grid design. It is called 3D because the guideway can be built under or over other things - especially other guideways. The most useful part of a 3D grid is that there are no intersections because the guideways can cross over or under other parts of the guideway so that no stops are necessary - much like freeway overpasses allow the cars on the freeway to continue non-stop.

Sytran/UniModal can be build in any guideway configuration. The guideway could be suspended on the side, or over, a street, it could be suspended on the side of buildings, it could travel up buildings. The guideway could also be a pair of lines going to and from two points, or it could be a huge grid system allowing transportation to anywhere on the grid (much like the road system).

Ideally, Skytran/UniModal would be built in a grid configuration, where parallel guideways would be built one mile apart and portals would be build every mile along each guideway. This configuration would require a maximum 1/2 mile distance to the nearest portal, and an average distance of 800 feet (about a 3 minute walk at 3 mph walking speed).

Decelerate - tracks, and brakes

On all PRT systems, vehicles slow and then stop on deceleration tracks (like turn-outs), similar to the way cars do on a freeway, rather than remaining on the tracks. All vehicles on a PRT main track travel at the same speed, and only slow on designated declaration tracks. High speeds normally require increased "headway", or stopping distance, in which vehicles (such as, say, a train) slow down on the main track - other vehicles normally need to be far enough behind to allow the vehicle in front of it to slow AND exit the main tracks. This reduces the number of vehicles per hour on a track. With PRT, this is not a problem.

Unimodal's braking would normally use regenerative brakes that convert the pod's momentum back into electricity. The emergency brake, however, would be a pad that presses against the inside of the steel rail, permitting fast (6G) emergency deceleration. This allows the UniModal pods to comply with rail safety standards requiring that a public transportation vehicle to be far enough behind the vehicle in front of it to make a complete stop in a very short distance. The high braking rates minimize the distance between cars, and permit pods to be closer together than in other systems, meaning more cars can be on the guideway at the same time.

Note that this braking rate is considered unsafe for the general population by most authorities (see the discussion of Personal Rapid Transit), and that rail safety standards are not properly applied to PRT systems, which generally have a separated grade guideway that prevents collisions. Most PRT systems achieve close headways by coordinating PRT vehicles to slow in a synchronized fashion, at much lower decelerations (generally 0.5 G maximum).

Pods are able to travel 72 feet (or about 1/2 second) from each other (note that only one pod can be between support posts at a time, meaning supports need only be able to support the weight of one pod - a max of 900 pounds)

The pods have seatbelts resembling race car seatbelts - with a wider belt and an X shaped harness - for maximum safety in emergencies.

Pods

The pods are aerodynamically designed for minimum friction to reduce power use and noise. The Unimodal pod design is 10 feet long, 200 pounds (passengerless)and is reported to have a calculated cost of less than $3000. The payload capacity of these pods would be 700 pounds. The pod is designed to carry two people in tandem (one behind the other) for decreased air drag. The average trip in the U.S. carries 1.16 people, so the idea is that having 2 people maximum per pod is not a problem for most trips. Since the system is designed to releive congestion, serving large families or groups is not a main goal of the UniModal system.

The advantage of such a small car is that it weighs less, and therefore requires less support (allowing a smaller, less expensive guideway). Larger groups could travel either in separate pods, or by other means of transportation (ie bus, car, train, etc - the system is designed not to replace these means, but to provide an excellent alternative). There are many reasons for this limited capacity: smaller cars mean cheaper cars, smaller and cheaper guideways, less air resistance on pods - lowering energy cost, and less wear on guideways meaning less maintenance cost. Making pods twice the size would most probably increase the cost of the system more than 2 or 3 fold.

The calculated cost for running a pod is one cent per mile, which translates into about 200 miles per gallon. The company plans to charge 10 cents per mile, about the cost of gas in a car (without all the other huge costs of a car), while giving the owners of the system a 1000% return.

The pods are designed for abuse, and can be pressure washed. The doors do not have handles (inside or out), but open automatically. The designers argue that handles are not only inconvenient in the general case, but are a huge danger in emergencies especially (people might be tempted to open the doors to a 30 foot drop to the ground). However, there is a door release mechanism on the outside of the pod to allow rescuers to open the door.

Resting pods roll on small wheels, but when the pods are accelerated to above around 2 mph, the pods are levitated by the Inductrack in the guideway. Obviously, after slowing to below 2 mph, the wheels act as landing gear to support the pod.

Batteries large enough to power a complete trip weigh too much to be in a pod. Pods would have a small battery, so that a pod could reach the next station and safely disembark its passenger even in complete system failure. Another proposed emergency power system would use small stationary, mass-produced turobogenerators powered by piped or stored natural gas, and mounted on every tenth pole.

Guideway

Land-use and right-of-way costs are minimized by mounting the guideways on poles more than 30 feet above the ground (30 feet is the design, but poles can be variably sized to accommodate other objects in the way). Unimodal's light-weight tracks are designed to permit smaller, less visually invasive, and more attractive installations than other types of transportation (the inventor points out most notably cars and trains).

Since the pods are light-weight, the guideways (the most expensive part of the system) can be made of light-weight, mass produced modular steel components. The expensive cement work is minimized, present in just the foundations of the poles.

Although the guideways have been reported to be about one million dollars per mile, more recent reports of about 2 million dollars per mile have been made. Inflation is a big factor in the cost of the guideway, however when comparing to freeways and trains, one can see that the guideways calculated cost is far less than the alternatives (roads cost about 8 million dollars per mile, limited-access expressways cost 30 million, and train tracks can cost upwards of 60 million dollars per mile).

One mile of guideway (both directions) has been reported to have a calculated capacity of 14'400 pods per hour (velocity * pod density = 100 mph * 2 pod/(72 feet) = 14'666 pods/hour).

Inductrack

Magnetic levitation permits low "friction" (present as magnetic drag) and linear force to drive the pods. Lawrence Livermore National Laboratory reports that at 100 mph, a 700 pound vehicle would require 408 watts (equivalent to .54 horsepower) to overcome the magnetic drag. By comparison, conventional cars (varying greatly around 3000 pounds) traveling at 65 mph consume between 3000 and 8000 watts. The system is designed to have hardly any moving parts and a pod in motion never comes in contact with the guideway. Therefore wear on parts should be very small - minimizing maintenance. Some benefits should be low friction, low track maintenance, and smooth motion with little track noise.

Since the guideway will use Inductrack, the system can still be used in a complete power outage (the passive maglev requires no power to levitate pods).

Intercity vs intracity travel

• Intracity travel is travel within a city. The plan would be to run these lines at 100 mph.
• Intercity travel is travel between cities. The plan would be to run these lines at 150 mph.

Due to air resistance, the energy costs of a vehicle increase as the cube of its speed. Therefore the intercity plan (at 150 mph) has energy costs 3.4 times as much per mile as the intracity plan (100 mph).

Other

The promoters refer to the system as "solid state". However, wheels are present for use during starting and stopping, and the doors move, as well as any moving conveniences such as fans to air from heaters or air conditioning units.

As in all PRT systems, fare-collection, driving and many maintenance tasks would be automated. Unimodal's design is to use simple speech recognition (not to be confused with voice recognition) for its user interface, rather than fare-cards or touch screens.

For each 90 degree turn onto a guideway perpendicular to the current guideway, there will be a deceleration track, turn track, and an acceleration guideway. The pod would decelerate to 20 mph during the turn, and then accelerate back up to 100 mph to enter the main guideway again.

Naming - Portal and Pod

The names portal and pod may seem strange to people, but the reasons for these words are purely psychological. People associate the words "station", and "stop" with buses, trains, long waits. People also associate cars with traffic, insurance, crashes, and gas prices. many of these connections may be unconsciously thought of and for these reasons, new words have been created to describe a system in which these connections are not present.

External links

• http://www.unimodal.com
• http://www.skytran.net

See also

Personal Rapid Transit is the generic term for a family of similar systems.

• Vehicles
• Transportation