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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 electric linear propulsion and a form of passive magnetic levitation called Inductrack.

The UniModal design is significantly different from other PRT systems. vehicles are suspended from an overhead track, vehicles are aerodynamically streamlined, and the system uses passive magnetic levitation. Also, the system is proposed to use speech recognition to interact with riders.

The system is designed to have very few moving parts (for economic reasons), the main moving part being the vehicle itself. 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.

Guideway

Guideways would be mounted on poles about 30 feet above the ground (industrial poles can be variably sized to accommodate a range of conditions). The guideways would be made of modular steel components, attached to a cemented foundations. One mile of guideway (both directions) has been reported to have a calculated capacity of 14'400 pods per hour.

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. Currently, the company says they are claiming $10 million per mile, but say that the reason for this is to make their cost analysis seem more believable, and they hold that their actual estimates are still well below that amount.

Pods

• 10 feet long
• 200 pounds (passengerless)
• estimated cost: ~ $3000
• Payload weight capacity: 700 pounds
• estimated running cost: $0.01 per mile (~ 200 mi/gallon)

The pods are aerodynamically designed for minimum friction to reduce power use and noise. The pod is designed to carry two people in tandem (one behind the other) for decreased air drag. The pods are designed to be pressure washed. The company plans to charge 10 cents per mile, about the cost of gas in a car.

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

Semantics

A Pod is the name of the vehicles in the UniModal system. The reasons for the name are psychological - people associate "cars" with traffic, insurance, crashes, and gas prices. The name pod is meant to reduce these connotations.

Portals are stair-structures where people get on an off pods. Since people associate the words "station" and "stop" with buses, trains, and long waits, the word portal is again used to avoid these connotations.

Guideways are the "tracks" that the pods travel on. This word is used in many PRT proposals, probably also for psychological reasons.

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.

Importance of weight and speed

The advantage of a small vehicle is that it weighs less, and therefore requires less support - allowing a smaller, less expensive guideway. Also, smaller cars are cheaper to build and have less aerodynamic drag. Making pods twice the size would most probably increase the cost of the system more than 2 or 3 fold. The system is designed to relieve commuter congestion - the main reason that the average car in the U.S. carries 1.16 people.

One advantage of Unimodal's high speeds is that trips would be faster. Another important reason to have higher speeds is that higher speeds increase capacity - a singly pod could be used more times in, say, an hour. This is a factor in saving money because the only other ways to increase capacity are to build more guideways, or more vehicles.

System Description

Hypothetical Trip

A person would approach a portal, 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 main reason to have such a grid is to avoid intersections - 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.

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).

Although a guideway grid would be most convenient for users, and most efficient for the system, the UniModal design permits guideways to be used in any configuration - such as a linear route system (like most train routes).

Decelerate - tracks, and brakes

Like all PRT systems, vehicles exit the main guideway, then slow and then stop on deceleration tracks

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. Vehicles would exit the main guideway, then decelerate to 20 mph during the turn, and then accelerate back up to 100 mph to enter the main guideway again. This is analogous to the way cars exit a freeway, rather than remaining on the road). In this way, the main guideway can allow a constant speed.

Unimodal's braking would normally use regenerative brakes that convert the pod's kinetic energy back into electricity. However, the emergency brake would be a pad that presses against the inside of the steel rail, permitting fast emergency deceleration. The designers cite that a six G (about 59 ${\displaystyle m/s^{2}}$) deceleration would be safe in the short period of time (about 3/4 of a second). The deceleration rate allows a vehicle traveling at 100 mph to stop in less than 17 meters (56 feet).

This fast emergency braking would allow 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. Pods would be able to travel at one-second headways and still comply. The pods would have seatbelts resembling race car seatbelts - with a wider belt and an X shaped harness - to be safer in emergencies.

Note that rail safety standards do not yet apply to PRT systems, and that this braking rate is considered unsafe for the general population by most authorities.

Pods would travel 72 feet (or about 1/2 second) from each other. Since guideway supports are spaced 36 feet apart, only one pod can be between support posts at a time - meaning supports need only be able to support the weight of one pod.

Concerns about the disabled

SkyTran proposes that, instead of designing the system so disabled people can use it, it would be cheaper to gives these people door to door taxi service instead.

Inductrack

The magnetic levitation system would be the passive "Inductrack" system using Halbach arrays, as developed by physicist Richard Post at Lawrence Livermore Laboratories. Passive maglev requires no power to levitate vehicles.

Magnetic levitation permits low "friction" (present as magnetic drag). 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.

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 (approximately). Therefore the intercity plan (at 150 mph) has energy costs 3.4 times as much per mile as the intracity plan (100 mph).

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