Personal rapid transit: Difference between revisions

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Personal rapid transit (PRT) is an emerging transport mode that offers on-demand non-stop transportation between any two points on a network of specially built guideways. PRT has been reinvented many times.

PRT developers and advocates say that it will provide more convenient service than cars, with the social advantages of public transport, and low (excellent) environmental impact. Some advocates estimate PRT's per-mile costs as ranging between $0.10/mile (the cost of a moped) to $0.01/mile (a bicycle is $0.03/mi). Several PRT systems are in development, and several PRT designs have been safety-certified by government authorities. Transit using similar automated technologies is in regular operation, with some systems dating back to 1974. Systems include West Virginia Universityand Schiphol Airport. These are said to prove the viability of small-scale projects in dense, high traffic applications such as universities and airports. Some proponents say that these developments prove feasibility.

Several PRT proposals have failed when their final projected costs exceeded initial expectations. Other PRT projects have failed technically, some with large monetary losses, often when political needs, schedules or budgets interfered with a technical requirement. As of 2005, there are no true PRT systems in operation, which some detractors believe implies infeasibility. Detractors also claim that PRT diverts money from traditional transit projects. For these reasons, PRT is a controversial topic, and public discussion usually results in heated debate.

PRT is unfamiliiar, but can be compared to existing transportation methods. The following describes the intentions of developers; criticisms of these claims will be discussed below.

PRT's advocates say that with properties like these, PRT should solve urban transportation problems. They point to ridership simulations suggesting that PRT systems could absorb between 15% and 60% of vehicular traffic. However, PRT's detractors claim that many of these properties are illusory or exaggerated, and point to the continuing lack of any operational PRT systems as evidence of their claims.

The concept is said to have originated with Don Fichter, a city transportation planner, and author of a 1964 book entitled "Individualized Automated Transit in the City".

In the late 1960s, the Aerospace Corporation, a civilian arm of the U.S. Air Force, spent substantial time and money on PRT, and performed much of the early theoretical and systems analysis. However this corporation is wholly owned by the U.S. government, and may not sell to non-governmental customers. Members of the study team published in Scientific American in 1969, the first wide-spread publication of the concept. The team subsequently published a text on PRT entitled "Fundamentals of Personal Rapid Transit".

The Morgantown Personal Rapid Transit project has been in continuous operation at West Virginia University in Morgantown, West Virginia since 1975, with about 15,000 riders per day (as of 2003). 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. 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.

The Aramis project in Paris, by aerospace giant Matra, started in 1967, spent about 500 million francs, and was cancelled when it failed its qualification trials in November 1987. The designers tried to make Aramis work like a "virtual train," and incorrect control software caused cars to bump very hard.

In Germany, the Cabinentaxi project, a joint venture from Mannesmann Demag and MBB, created an extensive PRT development considered fully developed by the German Government and its safety authorities. This project was canceled when a scheduling mishap coincided with a mandatory budget cut by the German government.

Raytheon invested heavily in a system called PRT2000 in the 1990s, 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 University of Minnesota, and were purchased by Taxi2000.

The UniModal project proposes using magnetic levitation in solid-state vehicles that achieve speeds of 100 mph (161 km/h).

In 2002, 2getthere, a consortium of Frog Navigation Systems and Yamaha, operated "CyberCabs" at Holland's 2002 Floriade festival. These transported passengers up to 1.2 km on Big Spotters Hill. CyberCab is like a Golf cart, except it steers itself using "guidance points" embedded in the lane.

In 2003, Ford Research proposed a system called PRISM. It would use public guideways with privately-purchased but certified dual-mode vehicles. The vehicles are less than 600 kg (1200 lb), allowing small elevated guideways. They could use efficient centralized computer controls and power. The proposed vehicles brake with rubber-tired wheels, reducing guideway capacity by forcing larger inter-vehicle safe braking distances.

In January 2003, a prototype ULTra system from Advanced Transport Systems Ltd in Cardiff, Wales was certified to carry passengers by the UK Rail Inspectorate on its 1km test track. It undertook very successful passenger trials and has met all project milestones to 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 reliable and economical.

ULTra was recently (October, 2005) selected by BAA for London's Heathrow Airport. 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.

Vectus, a Korean/Swedish consortium, begins (2005) conctruction of a test track in Sweden.

Safety engineers employed by PRT companies say that travel via PRT systems should be ten thousand to one million times safer than via cars because of basic design improvements. Computer control is said to be 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. In the event of a total failure, a car can be pushed to a repair facility by another PRT vehicle.

Tracks and vehicles are timed to "miss" at intersections. Careful engineering at several projects has shown that less-expensive one-way, single-level loops can operate as safely and almost as quickly as systems with far more expensive dual-direction clover-leaf intersections.

The Morgantown PRT system (considered group rapid transit by PRT experts) has now completed 110 million injury-free passenger-miles. By comparison, regular transit injures about a hundred people on average in that many passenger miles.

Embarkation stations are on turnouts so by-passing vehicles can pass by at full speed. Systems can embark passengers as fast as buses or trains, but mass embarkation stations must have a turn-out for each one or two passenger queues.

Theoretically, car-parks (parking lots) can be far smaller for shopping centers, universities, stadiums and convention centers, freeing much valuable land. Roads or rails are required for heavy transport.

All vehicles are powered by electricity, so pollution is much less. Most systems plan multiply-redundant power supplies, from track-side batteries or natural-gas-powered generators. Stationary power reduces vehicle weights.

Some designers prefer solid-state electromagnetic line switching built into vehicles rather than the track, so that tracks stay in service. A track failure drastically degrades many systems' capacity. This also allows closer spacing of vehicles as no time delay is needed to allow the track to switch. Some systems like 2getthere and ULTra do not need switches since the automated steering system merely chooses which path to follow.

Some systems plan to group vehicles to carry large groups. This also can reduce aerodynamic drag. Groups (called "platoons" or "trains") could share an intercom and destination.

Some systems plan multiple types of vehicles. The smallest vehicles seat two, the largest six. Two has the lowest-per-mile track cost, and handles most trips (average ridership in cars is 1.16 persons per vehicle in the U.S.) Most systems provide for wheel-chair users, bicyclists and light cargo vehicles, sometimes with special vehicles. One study found that light cargo could enable feasibility in a port city.

Most systems have buttons in a vehicle, such as "let me talk to the operator," "take me to the nearest stop," "take me to the hospital," "take me to the police for help," and "this vehicle is too filthy to use."

Vandalism could be investigated from video of the car, reviewed when the button "this vehicle is too filthy to use." is pressed. The Morgantown System reports very little vandalism accredited to the short wait times and cctv monitoring of the stations.

Many PRT advocates claim that it will have a per-passenger trip costs between $0.01 and $0.10/mile ($0.006 and $0.06/km) -- somewhat cheaper to operate than a moped. However many transportation planners disbelieve the "ridiculously low" cost estimates of proponents, especially when cast in terms of cost per rider-mile. How capital costs are incorporated is a critical element in cost estimates, since PRT systems are capital-intensive with low operating costs compared to other technologies.

In all transit systems, vehicles are depreciated on a schedule that accounts for the average number of empty seats per vehicle, and the number of trips per day. This becomes a number called "capacity utilization." When it is higher, fares cover more of the costs of the transit equipment and operators.

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.

In PRT, the cost of capacity is less because fare collection, driving and security are automated. Also, PRT idles not seats, but whole vehicles. Idle vehicles should use less energy, and wear and so depreciate more slowly than active but empty vehicles.

Standard transit-planning assumptions concerning overhead per vehicle are said to fail in PRT systems. One major operating expense of bus and light rail systems is the operators' and mechanics' salaries. Additionally, some systems require transit police as well.

PRT systems eliminate driver salaries by automating guidance and fare-collection. Repairs are far less per vehicle because PRTs have electric motors, with one moving part (on most the only moving parts are wheels and the door), versus hundreds for an internal combustion engine.

Transit police are not required because riders are not forced to share a cabin, and criminals cannot easily predict where vehicles will go, and so cannot wait for commuters.

The WVU PRT project failed commercially (though succeeding technically) because its track had to be heated to eliminate snow. Systems where the vehicles ride atop the track therefore try not to collect precipitation or dust. Weather is better handled by overhead tracks. Note that in this area, well-designed PRT systems can save money over conventional streets and vehicles.

As for fuel, PRT systems can be powered from the track, and purchase power from the cheapest electric utility. Unlike trains and electric buses, PRTs only accelerate and stop once per passenger, saving substantial energy. Ordinary electric motors are 98% efficient, and non-polluting. Some PRT designers have reported or projected energy usage of less than 900 BTU per passenger mile, compared to over 3,200 BTU per passenger mile for rail transit.

Still, it is well-known 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, which of course lack paid operators.

Some authorities say that even if PRT has the same costs, the increased load factor (O&M/passengers per destination) of PRT (about 0.33) should reduce costs per passenger mile compared to those of other public transit (which are about 0.15).

Another dispute concerns capacity utilization, which directly affects a transit-system's return on investment.

If the peak speeds of PRT and a train are the same, a well-designed PRT is two to three times as fast for a passenger as a well-designed bus or train route, just because the PRT vehicles do not stop every few hundred yards to let passengers on and off.

Therefore for the same maximum speed, PRT theoretically has two to three times as many trips per seat as a bus or train. So PRT should utilize its average seat 50 to 300 % more efficiently. This is contested, of course.

Such high route utilizations would let PRT replace a train or high-capacity bus route. If true, PRT could be used in an intermodal transport system, and then expand from a proof-of-concept project into a network.

PRT automatically diverts vehicles to busy routes and travels nonstop at maximum speeds. Simulations with standard assumptions show that at these high speeds, vehicles can be recycled for new trips as much as several times per hour, even during busy periods, even in low-density cities. This yields more trips per hour per vehicle, increasing ridership substantially during rush hour. In simulations of rush hour or high-traffic events like professional sports events, about 1/3 of vehicles on the guideway need to be empty to get the best response time.

At idle times fast speeds do not increase ridership, because no-one wants to travel. However, the higher ridership during rush hour lets a smaller fleet serve the same number of passengers. The result is therefore to reduce the absolute fleet size, and the number of idled vehicles during idle times.

PRT vehicles carry only two to four passengers in order to reduce weight. However, this also increases ridership per vehicle, because during idle times every operating vehicle will have a higher ridership (25-50%) than a mass-transit vehicle such as a bus or train (as low as 2% after midnight, 15% during non-rush hours).

Since the U.S. averages 1.16 persons per automobile in commuter areas, many authorities say that the optimum vehicle size in the U.S. for PRT is either 1 or 2 passengers. Some systems (UniModal, Ford Research's PRISM) have found that the weight and cost difference between these sizes of vehicles is so low that two seats is optimum, with tandem seating and a low drag shape.

Other authorities question the viability of systems with only two seats. The public's worst-case needs are shown by its choice of automobiles, 85% of which have four seats plus or minus one. Groups of three or four commonly travel together. Families with young children may be reluctant to split up. Also a person in a wheelchair with a companion and luggage may not be accommodated. Some PRT vendors therefore have chosen vehicles accommodating three or four passengers with luggage.

The spacing of PRT vehicles on the guideway sets the rate at which the guideway, the major system expense, can be depreciated by traffic. Designers therefore attempt to minimize the headway, the distance between vehicles.

Some PRT designers have planned for very short headways, which can allow a single guideway to carry the same number of passenger miles as four freeway lanes. This dramatically increases the capacity utilization of a heavily-used guideway, and substantially speeds trips through the center of a city, by permitting more use of direct routes. It also permits a PRT guideway to achieve carrying capacities similar to light rail.

Short headways are theoretically possible. PRT vehicles normally operate on unshared guideways, on a separate grade from other traffic. This means that emergency braking for side traffic is not required. Since the front vehicle will also be braking, the minimum safe distance between the vehicles will be set by the reaction time of the following vehicle. In most cases, this consists of the brake's mechanical reaction time, and the reaction time of the electronic control system. If the front vehicle electronically signals the following vehicle, and both vehicles use brakes with the same reaction time, the headway might be cut to the on-board computer's response time, which can easily be less than a fiftieth of a second. Even with large safety margins, this permits much closer spacing than the two-second headways normally used with cars.

Very short headways are very 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. Most authorities say that regulators may be willing to reduce headways with increased operational PRT experience.

Some persons calculate headways in terms of absolute stopping distances, using vehicle decelerations taken from rail lines, and then prove that PRT systems are impossibly uneconomic. This method of calculation is traditional in heavy rail systems, because heavy rail normally shares its grade with other traffic and has poor reaction times and very poor brakes compared to vehicle weight. These conditions do not apply to PRT. Some authorities argue that even when used for heavy rail, calculating headways from absolute stopping distance is too conservative.

Simulations with standard assumptions show that PRT, which should be substantially faster than autos in areas with traffic jams, should attract between 35% and 60% of automobile users. In contrast, new light rail systems and bus lines normally attract about 2% of automobile users, both in reality, and in similar simulations.

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.

The ridership simulations are disparaged, but have been repeated many times. If true, the high riderships would substantially decrease the cost per rider of PRT compared to trains and buses.

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). However, a typical light-rail right-of-way is 100 to 300 feet (30 to 100 m) wide, and (naturally) goes through the highest-density, most valuable part of the city. When the railway tunnels to conserve the surface, it becomes even more costly.

The surprisingly cheap, less than $1 million per mile estimates (2002, Orange County, California) of PRT designers depend on dual-use rights of way. By mounting the transit system on narrow poles, placed on an existing street, PRT designers hope to use land very economically. Small PRT vehicles with passengers can weigh as little as 1,000 pounds (450 kg), while conventional rail systems with many passengers often weigh tens or hundreds of thousands of pounds.

In some circumstances, such as at airports, 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). Even when account is taken of the need for two PRT guideways to match the capacity of one APM guideway, the tunnel volume (hence cost) will be less than half.

PRT rights of way may even cost less than a conventional road system. Proponents say that if auto- and bus-based transit systems include the costs of the roadways needed for buses and automobiles (US $10x10^6 per mile, or $6x10^6 per km), PRT systems are substantially cheaper than bus and automobile systems.

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 turn-out lengths (see below). Elevated tracks can "vertically merge" and keep to a narrow right of way.

Since systems have minimal waiting times, embarkation stations are very small (inexpensive) and lack amenities such as seating or restrooms. Usually there's only a fare vending machine, a gate or two, a line of vehicles and a security camera. The stations are usually mounted on poles with the track, but may also be inside buildings or at street level. In the U.S., systems must provide service to disabled persons. Some advocates say that a bus system to provide free disabled service is cheaper than elevators at each embarkation station, and this meets legal requirements, but this is an untested legal theory.

About 1/3 of the vehicles can be stored at stations, waiting for passengers. Storage facilities need very little space, because the vehicles are automated and interchangeable, so less space is needed for access lanes to pick out particular vehicles or to hold vehicles of different sizes.

The debate continues over the best guideway for PRT systems. Most systems' guideways are incompatible with both each other and existing transportation technologies. No technology has been acknowledged by all authorities as clearly superior.

Structurally, some guideway designs are 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.

Some points of agreement exist: it should permit fast switching and good braking, be inexpensive, be capable of being elevated, and pleasant to look-at. Ideally, it should not need to be cleared of dust or snow, and able to be built at ground level. Most systems also use the guideway to distribute power, data, and routing indications to the vehicles.

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.

Designing a power rail for all weather conditions is difficult. For example, glare ice can almost insulate a rail from a vehicle's brushes.

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.

The vehicle weight is so critical to capital costs and visual appearance that exotic aerospace techniques can usefully reduce the cost and size of both the vehicle and track.

Most designs put the vehicle on top of the track, because people prefer it. This also makes the poles shorter, with a smaller silhouette. They are said to be stronger and less expensive. Top mounted vehicles are said to unload the skins of the vehicle, which can therefore be lighter. Vehicles on top of tracks also have simpler line-switching, and in low density areas, can be inexpensively mounted on the ground without poles.

Design teams have used similar justifications for cars suspended (dangling) from an overhead track. Cars are said to be stressed in tension, "making a lighter vehicle structure" because many materials are stronger in tension. An overhead track is necessarily higher, and therefore more visible, but also narrower, and therefore creates less shadow, while having a small silhouette.

The least expensive real systems have used wheels with linear electric motors for drive and braking. To save money, the controls and electromagnets are mounted in the vehicles. Tight tolerance requirements in such systems can offset the structural cost savings. Taxi 2000 eliminated vehicle suspensions by making running surfaces adjustable. The least expensive structure for an overhead guideway is a rail suspended from a cable (See the aerobus). The fastest (theoretical) system would use magnetic levitation, which had some breakthroughs in 2000. The lowest-energy real PRT vehicles have used air-cushion suspension and drive. Controlled vehicle speeds can avoid vibrations in the structures. Combinations seem possible.

Routing indicators are often bar codes laser-cut from steel plates, and read by the vehicles with non-contact magnetic sensors. This system is unaffected by dust or wear and gives high precision positions.

The larger number of vehicles does not increase costs. Costs of transit vehicles are relatively constant per passenger. While larger vehicles enclose more space, they are nearly hand-built. A fleet of smaller vehicles can be mass-produced, as the auto industry shows.

Dual mode systems utilize an existing traffic network, as well as special-purpose PRT guideways. The particular advantage of dual mode systems is that they use existing roads to provide a large initial network, thereby circumventing the initial downside of the network effects. A particular advantage is that dual mode operation can reduce the initial expense of the guideway network. In some cases, the guideway is just a cable buried in the street.

The dual mode concept permits a long-term migration toward PRT-like traffic systems, without large initial sacrifices or expense. For example, Ford's PRISM proposal would certify very small cars to permit PRT-like electric power, spacing and automation on a guideway. The same small cars could still operate on conventional roadways. However phased implementation of dual mode can be difficult. Who would go to the expense of buying a dual mode vehicle when only a short section of guideway was available?

A notable disadvantage is that any dual mode system's performance is limited by its compatibility with existing infrastructure. This is most important in the power source and braking. Another disadvantage is that it does nothing to reduce the number of vehicles in use and the need for parking. Dual mode vehicles will only be used a few times a day much like automobiles. On the other hand PRT vehicles will receive many reuses a day (up to about one hundred for short systems).

A system like Taxi 2000 is single mode because the vehicles are always used on the guideways, within the system, in a completely automatic mode. The Danish RUF system is dual mode because the vehicles can operate on guideways in an automatic mode, or leave the guideways and operate on city streets, with drivers controlling them. British Ultra is now single mode, but its promoters envision the possibility of making a dual mode version in the future.

Many of the disadvantages and/or advantages listed below apply to single mode systems but not dual mode systems, and vice versa.

There are several concerns about the appearance of a PRT system.

People near the guideway are most affected by its shadows. In this view, more sunlight is better, because the sunlight falling on the guideway is useless to people. So, guideways should have minimal horizontal structure.

Another view says that the guideway's visibility is most apparent in long sight lines. In this view, the silhouette of the guideway should be minimized.

Most planners assume that a competent industrial design will provide an attractive appearance for the PRT vehicle.

Tube-enclosed systems can be enclosed in special "bio lung" greenery, with zero visibility of moving vehicles.

One successful algorithm places vehicles in imaginary moving "slots" that go around the loops of track. Real vehicles are allocated a slot by track-side controllers. The on-board computers maintain their position by using a negative feedback loop to stay near the center of the commanded slot. The vehicles keep track of their position in the slot with on-board speedometers. These have slight measurement errors (about 1%), so to keep the vehicles from bumping, vehicles' position and speed estimates are adjusted as they pass control points on the tracks. The track-side controllers have to keep synchronized with each other, also. The controllers assure that every two moving slots have one vehicle. At intersections "merge" logic manages the four possible combinations.

A slight variation places vehicles on North-South tracks in odd-numbered slots, while East-West vehicles use even-numbered slots. This permits rapid automatic merges and crossing of traffic at intersections. On the straight-aways, adjacent vehicles spread-out, or close-up to reestablish the every-other-slot relation. The alternating slots double the stopping distance in most situations, increasing safety.

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. This has succeeded in full-scale simulations and small test tracks, and uses slightly less energy.

The turn-outs to slow down or speed up for stops can almost double the length of track. Designers often increase the distance between vehicles to trade off lower guideway capacity for shorter, cheaper turnouts. Another trick to reduce turn-out lengths (and expense) is to keep vehicles in bunches (sometimes called "platoons"), and then widen the gap behind a slowing vehicle, and speed up (from a stop) into the end of a bunch.

Vibrations in the guideway can add unnecessary mechanical stress, increasing the cost. Most real systems use vehicle speeds that minimize vibrations in the guideway. Some theoretical designs have explored the use of vehicles' motors to actively damp vibrations in the guideway.

• By design and definition PRT includes:

• Non-stop rides from origin to destination

• On demand transportation, meaning no schedules or waiting

• Travel is alone or in self-selected groups

• Grade separation

• Stations offline on sidings

• PRT systems have numerous design features to prevent accidents: grade-separated guideways, wheels captured by the track to prevent derailment, automated control (decentralized in most modern designs), redundant safety-critical parts, central power with backups, periodic, often automatic inspections of safety equipment. So, widespread use of them could prevent most accidents caused from cars, and provide more reliable service.

• In theory, PRT systems will not delay commuters with gridlock or traffic jams. This should make them more attractive than automobiles. Methods vary, but most designs plan to move at or near the maximum system speed more than 95% of the time, including at "rush hour." PRT systems offer transportation two to fifteen times faster than autos, buses or trains (depending on assumptions).

• Per unit of passenger-distance, the traits of PRT allow proponents cost-out PRT systems at 3-10% of automobiles.

• With reasonable assumptions, PRT systems are said to have better capital use than other systems. Compared to light rail, a single PRT line integrated into an existing multimodal transit system (not a PRT network) is said to have a comparable passenger capacity to a train or freeway, fifty-fold lower cost of rights of way, 60% more trips per seat, and as an automated system that does not require rides with strangers, substantially lower costs of ownership because it does not need drivers or transit police. If PRT captures more riders, uses semi-automated track-assembly or expands into a network, these effects multiply.

• Parking costs, and space are not required, because the vehicles remain in use. They also eliminate a need for a driver's license, gas, insurance or sobriety. Of course, temporary storage of vehicles requires some space (and thus cost), because at low ridership hours, not all vehicles would be in use. In any case, much less space is needed than in other transportation systems.

• In theory, PRTs' lower costs can be completely offset by fares, eliminating government subsidies and interesting private companies who would in turn compete to provide even better systems.

• Since most PRT ideas include automated vehicles, passengers can relax and do other things while riding.

• PRT could eliminate much of the world's urgent dependence on oil. Liquid fuels could be reserved for heavy transport. If the need for oil causes wars, this could save more lives and money than any other feature.

• PRT systems usually are projected to be built much faster than conventional transportation systems, in months rather than years.

• PRT systems usually operate from the electrical grid, and are therefore far less polluting and less expensive than even fuel-cell automobiles. Because it is electrically powered, pollution occurs at a power plant that can be more easily monitored or improved than automobiles.

• Transit police are not required. Criminals cannot wait for a vehicle to arrive, because they would not know the car's destination. Most designs include a panic button that takes the unit to a police station. Stops and (in some systems) vehicles would have video cameras.

• Because of network effects, PRT is not fully useful until it is widespread. In this view, a small PRT system will not attract demand because it does not go to many destinations, despite the obvious parallels to trains and buses. Many people say that only a large PRT can attract sufficient demand to be self-sustaining. How it could grow from a niche to a local or metropolitan network is unclear to these persons. Growth to a national network is thought especially unlikely.

• People cannot customize them to their tastes, and therefore rarely have anything approaching the enthusiasm shown for a new car. Therefore, PRT systems may be as unattractive as other public transit. At Morgantown, most students use, but casually despise the transportation system, and recount stories of its failures. Some joke that the term "PRT" is said to stand for "Pretty Retarded Train."

• A PRT system is said to have lower costs and automated operations. These could lead to simpler organizations and smaller staff at governmental transportation offices. This directly reduces the responsibility and authority of government officials, which in most civil service systems, reduces their pay. It does not offer much incentive to administrators to adopt it.

• Many authorities say that the cost of constructing and operating the system is unlikely to be as low as claimed. Some systems (such as Morgantown) have had much higher costs than planned (Morgantown has to use steam heat to keep its tracks free of snow). Any new technology has to climb a learning curve, and for every new system, promoters must make speculative claims when asserting low construction and operating costs. Historically, costs are underestimated on transit projects and demand overestimated. Further, methods of recovering unplanned cost overruns can cause political and public strife.

• Residents living near such a system could oppose unsightly towers holding an elevated rail system, as well as the guideway itself.

• PRT systems all incorporate the savings of mass production, but that involves large initial investment. New infrastructure is hard to build, particularly without the support of the community.

• PRT systems are proven, at least in the German Cabinentaxi, the Ultra system at Cardiff, Wales and West Virginia University. Ultra now has demonstrated cost figures.

• PRT proponents say that the system offers hope for solving transportation problems that conventional transit options cannot. Chicago is a low-density city with fully-realized train, freeway, and bus plans. These have failed, and the city is now (as of 2003) said to be investigating PRT.

• Using PRT could let an impoverished yet technical country leap-frog past many more-developed countries' congestion, safety and pollution problems.

• Simulations show that PRT squeezes the transportation of up to four-lanes of limited-access highway into the ground-space of poles spaced thirty feet apart. Laid in a grid with 1 mile or less of separation between parallel guideways and stations spaced three-quarters of a mile or less apart, it should solve most cities' traffic problems, enabling growth from the low densities at which autos are practical into the densities at which trains become practical.

• Should estimates of low PRT capital cost be realized, there would be less investment needing to be recouped. Therefore it is conceivable that PRT could be cost effective for even lower density areas, such as urban single-family residential zones. The implication for urban planners is that all areas within the PRT coverage area, of all densities, could be served by PRT in a cost effective way. A result is that policy decisions regarding land use and economic development/redevelopment could be made purely according to desired land uses and economic outcomes, irrespective of the operational needs of the transit system.

• Most planners say that no economically successful PRT system has been demonstrated, and there have been too many failures for government agencies to spend public funds.

• Transit planners normally evaluate a new transport method as part of an intermodal network. In these cases, a PRT line may compete against a rail or bus line. When operated in an intermodal transit network, PRT rarely realizes the travel time reductions advanced by proponents, because connections to other mass-transit modes are only possible when the other vehicle arrives. Infrequent transit is often the weakest link in an intermodal system. Timed connections between conventional mass-transit modes, though rare, can be more efficient than PRT intermodal use.

• The claims made by proponents depend on certain reasonable but nonstandard design features (see above). Many planners argue that if conservative ridership, operating expense ratios and inter-vehicle lead distances (for bus and train systems) are used, PRT systems are less attractive than bus and train systems.

• In transit planning with standard ratios, if PRT were built in an existing high density corridor, it would be less efficient than trains. Only if additional capacity were required in a low density corridor, would it be more efficient than a bus line or automobile, since the capital costs of streets are already sunk.

• The effects of vehicular recycling at rush hours are disputed by some transit planners, because they are simulations. Some skeptics have said that since gross capacities have to be comparable (because the same number of people are being transported in the same time), no advantage can occur. However, comparing capacity (people per hour), and capacity utilization (money per person per hour) is a fallacy.

• Some experienced advocates say that the chief problem is that PRT threatens existing livelihoods associated with cars, buses, trains and related services. Since the market in rapid transit has a limited (government) budget in each city, and existing options are the best-funded, existing options and organizations tend to win political battles. As of 2001, this may be changing, because existing options have been unable to solve traffic problems.

• The very high vehicle utilizations inherent to PRT (vehicles are usually carrying passengers at full speed, rather than parked), means that there might be less need for, and investment in private vehicles, and auxiliary private services such as repair and insurance. Although these are social advantages, they indirectly threaten the livelihoods of many persons, corporations, and industries.

• PRT studies use up valuable transit resources that could be used to improve existing transit systems, such as light rail transit (LRT).

• One passionate anti-PRT activist, cartoonist Ken Avidor, says: "Basically, PRT is a stalking horse for the highway construction industry. PRT proponents can say things that the highway boosters could never say, such as 'People don't like to ride with strangers.' This anti-transit propaganda divides and conquers the opposition to highway projects." See [1] for details.

• "Transit Systems Theory", J.E. Anderson, 2000
• "Fundamentals of Personal Rapid Transit", Irving, Bernstein and Buyan
• The classic reference is "Systems Analysis of Urban Transportation Systems," Scientific American, 1969, 221:19-27
• The foundational text: "Individualized Automated Transit in the City," Don Fichter, 1964

• Morgantown Personal Rapid Transit, 1975-present
• UniModal - This hanging maglev system claims fastest speeds, and lowest cost.

• ATRA, The Advanced Transit Association, a professional group
• Innovative Transportation Technologies web site by Jerry Schneider. Comprehensive descriptions of both personal rapid transit and dual mode transportation, as well as monorails and maglev. Many articles of historical interest. Many links to current projects at various levels of development. Includes a section on the PRT debate with correspondence from both sides.
• Open Directory: Personal Rapid Transit
• PRT Wiki
• Transportationet PRT from engineering and law point of view. Site by Oded Roth, member of Israeli Retzef ("continuity, continuum") team.
• A Review of the State of the Art in PRT Systems, J. E. Anderson; Journal of Advanced Transit 34:1(2000)

• 2getthere, Utrecht, NL, a subsidiary of Frog Navigation Systems, with applications in Rivium, Schiphol Airport, and Floriade 2002, in partnership with Yamaha AGV
• Ultra, Cardiff Wales, UK
• SkyWebExpress, Minneapolis, Minnesota, US. Working 3-person vehicle, wheeled undercarriage using linear motor, 18-meter sample guideway.
• MicroRail, from MegaRail Transportation, Fort Worth, Texas
• Postech, Pohang University, Korea
• Cabinlift, from the Cabinentaxi Project, Germany
• WVU's Morgantown PRT, West Virginia University, Morgantown, West Virginia, US (Boeing)
• Progressive Engineer: "Still in a Class of Its Own" (PRT system)
• [http://216.239.51.104/search?q=cache:4dB0k7kbCkMJ:www.cities21.org/morgantown_TRB_111504.pdf+%22morgantown%22+%22PRT%22+%22transportation%22&hl=en Morgantown People Mover � Updated Description: Transportation Research Board Annual Meeting, Washington, D.C, January 2005]

• UniModal, Maglev 100 mph (161 km/h), California, US; New Delhi, India
• UniModal's former web site/Skytran, Maglev 100 mph (161 km/h), California, US
• PRISMProposal for Individual Sustainable Mobility, dual mode, with some of the advantages of single mode.
• RUF, Dual-mode, Denmark
• Thuma, a flexible system for varying sizes of containers.
• Vectus - Has 385 meter test track under construction in Uppsala, Sweden. [2] Picture of test track. [3]
• Skycab - A Swedish concept (website and documents in Swedish), status as of June 2005 (translated)
• EcoTaxi - Finnish version of PRT, termed "Automated Goods & People Mover" (APGM).

• Personal Rapid Transit (PRT) or Personal Automated Transport (PAT) Quicklinks
• Get There Fast, Seattle, WA group
• CPRT, Citizens for Personal Rapid Transit, US national group
• Get On Board Personal Rapid Transit, Seattle, WA PRT news, analysis & education website.
• Skyloop
• [4] - A site analyzing Lightrail Now's report on PRT.
• Another Rebuttal - against Lightrail Now's report
• PRT IS A JOKE Is a Joke (satire)- Web site owned by a non-cartoonist supportive of PRT.
• Analysis of some of the anti-PRT arguments originated by Ken Avidor.

• Personal Rapid Transit PRT Skeptic Page - Web site owned by a cartoonist opposed to PRT.
• Cyberspace Dream Keeps Colliding with Reality - A web page from Lightrailnow.org, a pro-light rail advocacy group opposed to PRT.