PRT Consulting, Inc.
1340 Deerpath Trail, Suite 200
Franktown, CO 80116, USA

Efficient Transit Solutions
Personal Rapid Transit Pods

Frequently Asked Questions about Personal Rapid Transit

1. What sets PRT apart?

Unlike other guideway- or track-based systems, the track is fixed and never moves even at switches (merges and diverges). Switching is in the vehicle itself. This enables very close spacing between the vehicles enabling high capacities with small vehicles. It also facilitates offline stations (on sidings) which allow point-to-point nonstop travel. Unlike a train, stations can be added without any negative impact on through traffic. This allows numerous stations and keeps walking distances low.

While two-way guideway in a corridor can work, in most situations, PRT works better as a network of one-way interconnected guideways. This means stations can be located throughout the community rather than just along primary corridors.

PRT provides better service than other modes because:
  • Waiting times are short
  • Walking distances are short
  • Trips are quick (mostly nonstop)
  • All passengers are seated
  • Service can be 24/7

2. What is the difference between PRT, GRT and ATN?

PRT uses small vehicles (typically 2 – 6 passengers). Vehicles can usually be platooned together in twos or threes.

Group rapid transit (GRT) uses larger vehicles (typically 12 – 25 passengers). Larger vehicles can be a good solution when there are few stations. Once the number of stations exceeds about eight, either the vehicles have to stop frequently or most run half full.

Automated transit networks (ATN) is an umbrella term for PRT and GRT.

3. How can a pod be both lightweight and safe?

PRT pods are designed never to collide with each other so crash-worthiness is not required. In over 300 million passenger kilometers a pod collision has never caused a death.

4. Why is PRT inherently safe?

PRT vehicles operate on their own dedicated guideways and are separated from other traffic and pedestrians. There are no crossings, only merges and diverges.

5. Are pods wheelchair accessible?

All PRT pods presently in public service are. They are also accessible to bicycles.

6. How do pods merge at speed at intersections?

With a synchronous (point following) control system pods follow predefined virtual points. Points that merge with each other are never allowed both to be occupied. Each pod is assigned a predefined clear path through all merge points before leaving the station.

With an asynchronous (car following) control system pods follow each other maintaining a safe separation distance. Relative positions are sensed at intersections and pods adjust their positions, like cars on a freeway entrance ramp, in order to merge

7. What are the challenges in securing air rights?

Air rights are for aviation. PRT requires use of right-of-way just like a powerline. The owner/regulator of the right-of-way (typically for a road) must give their permission for PRT to share it. Aviation authorities must approve guideways located near airports or forming potential obstructions to aircraft flight.

8. How do you construct around trees and streetlights?

PRT alignments are more flexible and much narrower than those for elevated light rail or automated people movers. Nonetheless not all obstacles can be avoided, and some will need to be relocated or removed. Streetlights can be replaced with lights supported by the guideway.

9. How can you be sure the system can be scaled to a large size and capacity when existing deployments are much smaller?

First it should be understood that Morgantown (opened in 1975) has demonstrated capacity up to 5,000 passengers per hour per direction using antiquated technology. They put 3,000 an hour through one station on game days. PRT systems are designed with distributed (as opposed to centralized) control systems. It is easy enough to demonstrate hand-off from one zone to another.

10. Why has a large PRT deployment not happened before?

Largely because urban PRT is a system that is most viable in large deployments. It generally must be acquired by transportation agencies.

Imagine a person from 1925 who is placed in a room with a set of encyclopedias, a phone on a land line and a smart phone and asked to figure out how to get from their address to downtown using transit. Chances are they will try to use the encyclopedia or call somebody on the land line. There is no way they will even know how to turn the smart phone on. Our transit agencies are using train and bus technologies first deployed in the 19th century.

These systems still operate on the stagecoach model. A passenger has to get from their origin to the station miles away, then wait for a coach, then stop at every station along the way and finally get from a station to their final destination. By analogy, transportation consultants, transit agencies and politicians have mostly barely graduated to a land line. Only a few have thought to call somebody for instructions on how to use a smart phone. PRT was like a land-line phone when it first came out in the 1970s. Now it is more like a smart phone, but few understand that.

11. How can we be sure reliability, safety and capacity would work in a busy urban setting?

PRT operates on dedicated guideways separated from other traffic and pedestrians. Busy urban settings have no impact on it provided it can handle the passenger demand. All modern PRT systems achieve over 99.5% reliability – five times more reliable than transit level of service A.

PRT safety is well proven to far exceed that of all other surface transportation systems except automated people movers of which it is a subset.

Morgantown demonstrated 5,000 passengers per hour per direction (pphpd) with 22-passenger vehicles back in 1975. Vectus demonstrated 7,000 pphpd capabilities with six-passenger vehicles around 2008. Modern PRT systems will soon double these capacities or more now the American Society of Civil Engineers Automated People Mover Standards are being changed.

12. Wouldn't PRT capital and O&M costs be comparable to or even higher than automated people movers or light rail?

PRT column loading is approximately ten percent of that for automated people movers and light rail. Since guideways typically comprise more than half the capital costs, they can be expected to be much lower. Even assuming the costs were the same on a per-kilometre basis, PRT is much more cost-effective on a per-passenger basis, which is what matters. This is because many studies around the world show that the much higher level of service offered (short walking distances and waiting times coupled with higher average speeds enabled by nonstop travel) results in a ridership approximately four times higher.

Vehicle capital and operating costs are proportional to vehicle weights. Vehicle weight is in turn proportional to passenger capacity. Large vehicles have high costs balanced by high passenger-carrying capacity. However, the cost-effectiveness of large vehicle systems suffers because, during off-peak hours, many large vehicles must continue to circulate even though they are mostly empty. With small vehicle systems, most vehicles can be parked during off-peak hours.

13. Wouldn't adding PRT to the mix of available transit modes just mean another transfer?

Initially yes. Then as the PRT network grows people will find they can go anywhere on it nonstop and with no transfers. The legacy transit will continue to have transfers (even within the same mode) and attract some trips while the PRT system attracts many more trips. Use of cars will diminish as will congestion.

14. Aren't most so-called PRT systems in operation today more like shuttles that do not demonstrate PRT capabilities.

PRT and PRT-like systems in operation at Morgantown, USA; Rivium, The Netherlands; Heathrow Airport, UK; Masdar City, UAE; Suncheon, Korea; and in demonstration in Guadalajara, Mexico all demonstrate basic PRT functionality including:
  • Vehicle-mounted (as opposed to track-mounted) switching
  • Offline stations that can be bypassed if that is not the destination (the Vectus system can bypass the offline vehicle maintenance/storage facility)
  • Short headways (time between vehicles). Morgantown has demonstrated 15 second headways since 1975.

15. What happens if a traffic jam occurs at a merge?

Synchronous control systems avoid traffic jams on guideways by holding vehicles in stations until all merges needed for the trip have been secured. In the event of heavy demand, passengers are held in stations. This encourages and facilitates ridesharing and boosts system capacity when it is needed most.

Traffic jams on guideways can occur with asynchronous control systems. These systems must monitor traffic and divert around congestion where possible. They can also meter the amount of traffic leaving stations and heading towards congested areas. If a jam does occur, it will automatically clear itself as demand eases.

16. Why has the Masdar PRT System not been expanded beyond 13 vehicles even though it was planned for about a thousand vehicles?

The problem at Masdar City is the City design, not the PRT system which has performed flawlessly since day one and achieves over 99.7% reliability. Masdar City is designed to have the "ground level" be a concrete platform 20' above the desert. The streets at this level are designed to be discontinuous to reduce the desert winds blowing through the city.

This discontinuity is reflected into the basement below to which the PRT was relegated. For these and other reasons the PRT layout is unnecessarily circuitous and requires many slowdowns. The city planning team largely ignored the concerns of the PRT planning team. Furthermore, the concrete platform adds significantly to the development costs required to be invested before building lots can be sold. This has significantly delayed the expansion of the city and thus the need to expand the PRT system.

17. How can we be sure enough people will ride an urban PRT system?

People decide whether to use their car or go by bus, train, taxi or bicycle based on two primary factors (assuming all these modes are available to them):
  1. Cost
  2. Time
Since we can show PRT will cost less and take less time, we know more people will use it than use regular transit. Many studies around the world indicate that the percent using PRT will be significantly higher than that using conventional transit. These studies generally ignore additional factors such as that PRT is much safer (zero injury accidents in 300 million passenger kilometres) and more comfortable (everyone gets a seat).

18. How can lots of people be carried in a system using small vehicles?

The primary worldwide mode of transportation is a small vehicle. It is called the car or automobile. Cars carry billions of people every day. Using a small vehicle for public transportation is impractical when it requires a driver. Driverless small vehicles are the most practical and economical form of public transportation provided they are separated from other traffic and pedestrians. The paradigm changes when you remove the driver.

19. Can PRT be integrated to work with other modes such as trains, buses and taxis?

Absolutely! Most other modes, especially trains and bus rapid transit, function best in corridors. PRT functions best as a network of guideways spread throughout the service area. Thus, PRT can serve the areas between corridors and help bring passengers to the systems operating in the corridors. Studies show that adding PRT to the transit mix generally attracts additional riders to the PRT system as well as to the legacy transit systems – all transit modes tend to benefit.

20. What happens if a vehicle gets stuck on a guideway?

First, PRT suppliers work really hard to ensure this never happens. Vehicles monitor their own health and are removed from service at the first indication of an issue. Nonetheless, failure must be prepared for. A vehicle failing on a guideway can usually limp to the next station at a low speed. A vehicle stuck on a guideway will be pushed or pulled into the next station either by a following vehicle or a rescue vehicle backing down the guideway. If emergency vehicle evacuation is needed, passengers can be rescued by a truck-based crane or can lower themselves to the ground using an on-board escape chute.

21. What happens in the event of a power failure?

PRT systems must always have multiple power sources and key control computers must themselves be redundant with redundant back-up power sources.

22. What are the differences between a network of one-way loops and a network of two-way guideways?

One-way guideway infrastructure is smaller and less obtrusive. The station infrastructure is also simpler and smaller. A network of one-way loops can support a bigger service area with more small stations. Generally, the service area will be about 50% bigger for the same capital cost. One-way loops do result in some out-of-the-way travel but this usually only amounts to one or two minutes per trip. Two-way guideways work best for connecting a few stations along a corridor. In most other circumstances one-way loops work best. Complex layouts comprised of interconnecting two-way guideways require complex interchanges or speed- and capacity-limiting roundabouts.

23. What is the "network effect"?

Think of four bus lines, one going in each direction of north, south, east and west. Assume each line has four stops, one at the beginning and one at the end plus two where it intersects with the other lines. This layout will be a network with twelve stations. From any one station you will be able to get to eleven other stations. However, one or more transfers will be required to get to all but three of those destinations. A PRT layout could be similar but no transfers would be required because the small vehicles can all go to any station from any other station. Unlike a bus, they do not follow a predetermined route but go to whatever station the passenger requests.

Now let's think about the utility of this system. A line serving only two stations (one station pair) has only two points of origin and two points of destination and little utility. Few would use such a line. It can be assumed that the utility of a transit system is proportional to the number of station pairs in the system. The number of station pairs increases at approximately the rate of the square of the number of stations. Thus, a network system with no transfer requirements and with twice the number of stations will have about four times the utility and should attract four times the number of passengers. This is the network effect.

The twelve-station network described above would have 66 station pairs. If we double the number of stations to 24, the number of station pairs goes up to 276 (4.18 times more).

24. If the guideway is elevated, how do passengers get up to it?

PRT stations are accessed by stairs leading to a platform that is level with the vehicle floor (no step required to enter the vehicle). Most or all stations are equipped with lifts (elevators) and/or escalators to facilitate access by the handicapped.

In some circumstances it is possible to bring PRT stations down to grade to allow direct access from the sidewalk level. It is also possible to attach PRT stations to an upper floor of a building. Typically, the vehicle will stop outside the building adjacent to sliding doors in the building exterior wall. The vehicle doors will be synchronized to open simultaneously with the sliding doors and permit direct access to/from the interior of the building. The building's vertical circulation system can be used to access other floors.

25. The name "Personal Rapid Transit" and the high level of service provided implies a system intended for the elite. How will poor people afford it?

PRT systems can provide a tiered fare system. Premium fare will pay for the use of an entire pod for a party of up to six traveling together. They will typically wait less than a minute and travel nonstop to their destination. A standard fare will by a seat for one person. They may have to wait a few minutes to facilitate ridesharing and make an intermediate stop or two. Matching fares to the level of service provided enables PRT to provide good transport to the entire cross-section of the population.

26. How much space will this system take up?

Guideways are supported on columns of about 75 cm (18") in diameter placed about 20 m (60') apart. If stations are elevated, they too will have a small surface footprint for columns, stairs and elevators. The entire footprint will be less than one percent of the footprint of a bus rapid transit system and, in most cases, should fit within existing road reserves (rights of way).

27. How disruptive will construction be?

Typically, most construction elements will be manufactured offsite, shipped to site and assembled into final position. In many situations the construction will be taking place in or behind the sidewalk with some disruption of pedestrian traffic and little or no disruption of road traffic. In some situations, such as when the guideway is being placed in a narrow median, there may be the need to close one lane of traffic. Unlike road construction, the construction process is very quick and any disruption will not last long. In sensitive areas, construction could be limited to night time only.

28. Does the entire network have to be completed before any portion is opened to traffic?

No. As soon as one loop with more than one station is completed, it can be opened to traffic. As more loops are finished, they can be added to the network. This is the preferred way of opening the system to the public. It allows the public and the operators to build confidence in the system starting small and expanding over a number of years.

29. Can an initial pilot system be built to demonstrate how the system works and see if people will use it?

Yes. However, it must be understood that a pilot system with few station pairs will generate little traffic and may therefore appear to be a failure. In addition, it is unlikely to be financially viable and if expansion of the system has to wait for the pilot system to be approved, private financing will likely not be available for the pilot system.

30. What are the government costs involved in building a large PRT deployment?

Relatively little. Typically, the government will pay for a feasibility study to ensure the project is viable and does not include undue risk. Then a PRT developer will raise private financing to build the project. In addition to paying for the study, the government will usually also provide permission for the PRT infrastructure to be located in existing road reserves and assist in obtaining additional land in the few instances where it is needed. The government will usually also relocate utilities that the system is unable to avoid. Finally, the government may guarantee minimum revenues and/or agree to help ensure ridership by managing the use of competitive modes.