Ultimate Personal Rapid Transit (UPRT): An Initial Concept Definition
This overview has been compiled and edited by Jerry
Schneider from postings by James Leon, Gordon
Peterson and the author to the < transit-alternatives >
list during 1995. It is intended to help people who join the transit-alternatives list to
learn about the UPRT concept. The term UPRT was suggested originally by Palle Jensen. Most
of the ideas about the UPRT concept have come from Gordon Peterson. Persons wishing
to know more about Gordon can review his home page
UPRT is viewed as a total replacement for the conventional automobile and its
associated facilities and services, in urban/suburban areas. It would use an extensive
(dense mesh), exclusive guideway system to carry small, private and public, very
light-weight and relatively inexpensive vehicles. The vehicles would be passive and would
contain no drive, suspension or steering components. Every effort would be made to
[re]move active and complex mechanical components from the vehicle and place them into the
active guideway. Riders would have no control over or responsibility for guiding the
All branch switching and acceleration would be controlled externally by a collection
of networked computers. Each section ofthe guideway (probably a small section) would be
controlled by a computer module which would be manufactured as part of that guideway
module. These modules would be mass-produced in highly automated factories and assembled
on-site, LEGO-style. The guideway would be elevated (typically) and would contain all of
the equipment needed for both propelling and switching the vehicles.
Linear induction motors might be used for propulsion on most of the guideways but
rollers ... or even driven wheels/tires contained in the guideway (with the vehicle able
to roll across the tops of these wheels) might also be used. Such a rotating wheel could
perhaps be mounted in turn on a rotating base arrangement, which would allow driving the
vehicle in any direction desired. The vehicle need not know or care how it is moved, and
the actual drive and suspension systems might well vary from one section of the guideway
to another. Even a conveyer belt might be used for low-capacity sections. Other types of
electric propulsion systems might also be possible.
The vehicle configuration might be circular, because circular things are inherently
strong and have a minimum surface area for the volume they contain. They are also simple
and lend themselves to inexpensive and easy-to-robotize assembly processes. Also, human
forms are wider at the hips than at the feet. Putting the seating area around the
periphery of the vehicle's interior maximizes hip room and orients the less-bulky knees
and feet toward the center of the vehicle.
It has been suggested that the vehicle have a diameter of about 12 feet and that it
not look like a conventional auto in any way. It might resemble something vaguely like a
circular version of the Renault-conceived (for EuroDisneyland) "Reinastella"
vehicle. This vehicle can be seen at the "Transportarium" attraction at American
Disney parks, near the end of the film. It's the vehicle in which the "time
travelers" sent by Timekeeper overfly Paris.
The bottom of the vehicle could be a "skid-type flat platform" with no
wheels or suspension. The vehicle would be capable of making 90 degree turns after coming
to a complete stop. The vehicle would not be rotated when it goes around a corner. It
would be able to stop moving in one direction and move away from the stop in a different
The switching mechanism would be faster than a switch on-board the vehicle, allowing
for a very short headways. The switching mechanism would not have any moving parts other
than the vehicle (and it supporting wheels in the guideway) and would be very fast and
extremely reliable. The control system would release vehicles from an origin only when
clear passage all the way into the destination was available. A decentralized control
system consisting of a large number of networked computers would provide vehicle and
routing control for the entire system. The control system would be similar to that used in
telecommunications systems rather than that used in conventional transit systems.
The vehicles would be very inexpensive because they would be essentially a hollow
elliptical sphere. Interior furnishings would be strictly a matter of function and
comfort,and would only minimally be affected by mechanical considerations. The A/C and
heating/ventilating systems would be essentialy the only mechanical equipment carried in
The guideway would be similarly inexpensive because of high volume production
economies. The guideways would form an areawide "closely spaced mesh" capable of
moving passive vehicles from any origin to any destination. All (or most) of the
intersections on the mesh would be at grade and vehicles would be controlled,
guideway-segment-by-guideway-segment until they reach their destination. The computers
involved would know where every vehicle in the system is at all times (even those that are
not moving but are parked). They would also know the status (occupied or unoccupied) of
every "slot" or "space" on the guideways at all times. Status
information about moving vehicles would include its speed, direction and perhaps its final
A person who wishes to go from A to B would indicates this desire with a smart card
(or some similar system) upon entering the vehicle. Then, the computers would give a go
signal when an entire route to the destination is available. The vehicle would move out
(perhaps on a conveyor belt) and be placed onto an adjacent guideway segment to begin its
No collision problems would occur at intersections because it would be impossible for
two vehicles to arrive at an intersection at the same time. This applies to all types of
intersections (i.e. 2-leg, 3-leg, 4-leg or more). Each vehicle moving on the system would
be assigned to a moving slot which would move at a constant speed. Or, perhaps the speed
would need to be variable within some range or without restriction. The computers involved
would be networked so that any information needed about vehicle X on guideway A could be
obtained when and where needed. Passengers could communicate with the computer system so
that they can change their destinations enroute, if absolutely necessary. Fault tolerant
computing would be used extensively and there would considerable redundancy in the system.
Empty vehicles could be moved about in the same manner - it would not matter to the
computer system if they are occupied or not. Automated goods movement would also be
possible. If communication between vehicles was required, it could be either by wire or be
wireless (cellular or satellite mode).
Each computer control module only has to worry about its one portion of guideway, and
doesn't know or care about other non-adjacent sections of the guideway. This is a basic
principle that makes the system scaleable, so one can keep adding to it any time and as
much as is needed (e.g. like Internet, or the worldwide telephone system).
Before the journey begins, the user would have to have a complete journey scheduled
and itinerary approved by the control system all the way through to the proposed
destination. This "approval" basically involves reserving a moving
"patch" of guideway big enough to hold a vehicle, traveling at the designated
speed , all the way through to the destination. This reserved "patch" would
cross intersections and slow down at places where the vehicle would be transferred from
one guideway to another (these turns would be minimized by the routing algorithm as much
as possible, since they represent both a delay and a loss of momentum).
A complete itinerary would be reserved all the way through to the final destination so
that a vehicle would not start a journey and then find out, once enroute, that it simply
could not complete the journey as expected. It would be possible to request a change in
the itinerary once enroute (in particular, if necessary due to a medical emergency or
something) but in a truly worst-case situation, under pathologically difficult loading
conditions, one might theoretically still have to complete the originally planned
itinerary, and then request a new one to the revised destination. As a general rule, the
routing would not be adjusted once the vehicle was enroute, other than on an emergency
The routing would be like that used for a long-distance telephone call. In the
worldwide telephone system, routing is determined (usually in a few seconds) by the
computers that control it at the beginning of the call, before the distant telephone
starts to ring. Similarly, the entire route would be determined before a UPRT vehicle
starts to move.
It is not thought likely that a secondary routing would have to be used very often,
but it might be on occasion. In the event of a problem reserving a space on a given
section of guideway, or through a particularly overloaded intersection, that section or
intersection could either be avoided entirely and an alternate route taken. Or (if there
is an available clear path through within a few seconds of the requested time, and if the
absence of immediately adjacent vehicles on the same preceding guideway allows) the
preceding guideway might adjust the speed of that specific vehicle (up or down) slightly
so as to allow the vehicle to use that available space.
Under normal service situations it is not clear that it is desirable or necessary to
worry a lot about global control issues. The great majority of the service issues would
arise and be resolved locally, just like the telephone system, or Internet. A local
Internet server does not have to know or care how a message is going to be routed from the
U.S. to Australia. All the local server has to worry about is the next computer downstream
since it assumes responsibility once the message packet is handed off to it. That is the
totality of its functionality.
There is no particular theoretical difficulty of doing "on the fly" route
changes, but it's not something that ought to be encouraged. In fact, it should be
discouraged, since it's analogous to someone reserving seats on hundreds of different
airplanes under different bogus names for the same trip ... space is blocked that might
have been used by somebody else, and which will likely not be released soon enough to
allow it to be used).
Normally, there would be no real communication "between vehicles" required.
However, continuous communication of the desired destination from the vehicle to the
guideway, and the associated negotiation between the computers regarding the route, would
be required. This can be done by very simple low-powered RF communication, much like
wireless intercoms or walkie-talkies or cordless telephones use, since the distances
involved (vehicle to guideway antenna) would be quite short, probably less than 100 feet.
Vehicles could carry other kinds of communications and entertainment equipment,
including cellular telephones and, perhaps even satellite communications, but these would
be for passenger convenience and connectivity only and not required by the UPRT system
More information on this UPRT concept can be found at Gordon Peterson's website .
Last modified: March 19, 2004