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The Center for Sustainable Infrastructure Blog

What is Personal Rapid Transit?

February 12th, 2016 · No Comments · Transportation

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By Julie Rodwell – Guest Contributor

The idea behind Personal Rapid Transit (PRT) arose in the 1950s and was focused on how to get people out of their cars and into transit by creating a suburban, low density transit system that would be as attractive and quick as driving oneself.

The vision is a small, private driverless car to take you direct to your destination at the push of a button.  The car runs on a system that bypasses other stops en route and goes just to yours. PRT concepts can be gondola-type systems, with the cars suspended, or guideway-based systems.. Retired University of Washington Professor Jerry Schneider provides a good summary of both suspended and guideway systems on his web site. His overview of technologies and systems provides the status of systems around the world.  The Wikipedia entry on PRT provides another excellent source.

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The separate guideway is to provide grade separation, that is, the ability for the PRT system to run above or below grade and therefore not mix with street traffic, avoiding the delays that can be caused by congestion.

In the Masdar PRT vision, the guiding magnets are embedded in the street, where no other vehicles are allowed:

… a driverless fleet of 3,000 free-moving, electric vehicles would transport 2 to 6 passengers between 85 to 100 stations, tallying up to 135,000 trips a day along preprogrammed routes. …. A wi-fi network would maneuver the podcars through obstacles in real time as magnets along the path continuously pull the vehicle into alignment …2getthere, Masdar’s provider had its contract extended recently.

Around the world in the past few decades, many vendors have taken a look at pursuing the PRT concept. Right now there are only three suppliers in the world that are market-ready or nearly so. They are 2getthere in the Netherlands, Sky Cube (aka Vectus) in S. Korea and Modutram in Mexico (almost there).

Comparison with Conventional Rail Transit

Traditional rail mass transit uses large heavy cars holding a couple of hundred people.  These systems work best in high density corridors (a million people or more).. They are often radial systems, going from an outlying area to a central city, or they may be loop systems, serving a number of stops on the edge of the central city. The guideways are large and the train frequency is not usually very high – 5 to 10 minutes at peak times.  Passengers must endure stop-and-start operations as people get on and off at stations they don’t want.

By contrast, PRT is conceived as a more suburban application, with smaller cars, a lighter guideway, and the ability for cars to come with headways (the time between cars) as low as 4-6 seconds. This high frequency, along with privacy and direct routing, are the ways that PRT is able to compete with private cars.

Even back in the 60s a computer-operated control system was part of the concept, for to be appealing to riders, PRT cars would need to come along very rapidly or already be waiting in the offline stations to serve the next party as they arrived.  Since computer sophistication is so much greater in 2016 than the 1960s, PRT was premature until computers caught up. Having GPS in the public domain also plays a role in facilitating PRT.

Origins

PRT’s first governmental support in the U.S. was by the Nixon Administration, in the 1960s, around the time that the Urban Mass Transportation Administration (now the Federal Transit Administration) was formed.   Public funding in the U.S. has not been forthcoming however, in part due to objections from the mass transit (heavy rail) sector.

Systems in Place Today

A driverless guideway transit system, currently being upgraded was built in Morgantown, West Virginia in the 1970s to serve the campus of the West Virginia University.  Known as “the PRT”, this is actually Group Rapid Transit (GRT) as the cars hold 20 people and generally stop at all stations.

PRT built by Ultra PRT is in operation at London’s Heathrow Airport in the U.K.  It is successful but has yet to be expanded to the full system initially envisaged.

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Courtesy Ultra Global Ltd.

UltraPRT said in 2013: Here, Ultra’s first commercially operational pod system provides 800 passengers per day with a vital link between the T5 Business Car Park and the terminal itself. A powerful example of the system’s benefits, the small footprint of the Heathrow pods system enables it to fit within the tight constraints imposed by the airport infrastructure. Commissioned by Heathrow Airport operator BAA, the system consists of 21 vehicles, a total of 3.8 kilometers of one-way guideway, and three stations – two in the T5 Business Car Park and one at Terminal 5. To date the system has carried over 700,000 passengers and in May 2013 celebrated reaching its 1 millionth autonomously driven mile.

However, Ultra has closed down. Heathrow purchased their system and is keeping it in operation. The British government has initiated a test program that will use modified Ultra vehicles on the street.

Masdar’s initial concept was the most ambitious:

The initial goal of Masdar City was to have a “street” level that was a large vehicle-free pedestrian zone. Ultimately, the high cost of building the entire city on top of a platform to accommodate the podcar system was too costly. With the passing of Masdar City’s solution to personalized transport, another of the three initiatives dies as well. Masdar City’s plan involved using the same dedicated guideways to run two-pallet flatbed vehicles as part of a Freight Rapid Transit program. The entire system was designed to run up to 5,000 trips per day, with each of the 810 vehicles having a maximum payload of 1,600 kg, delivering all necessities to residents and businesses.

The Masdar  system has been reduced from the original concept:

In October 2010 it was announced the PRT would not expand beyond the pilot scheme due to the cost of creating the undercroft to segregate the system from pedestrian traffic.

Plans now include electric cars and electric buses. In June 2013 a representative of the builder 2getthere said the freight vehicles had still not been put into service because they had not worked out how to get freight to and from the stations.

Skycube by Vectus opened its 5-kilometer, two station PRT system recently in Suncheon Bay, South Korea.  It has an elevated guideway, third rail electric power and four-seater pod cars

PRT Has More Failures Than Successes?

Many PRT studies and mockups have been created that have not led to implementation. In the 1990s, a three-mile PRT project was to be built in the Town of Rosemont adjacent to O’Hare Airport by Raytheon in partnership with greater Chicago’s Regional Transportation Authority (RTA). The RTA is the second largest transit agency in the nation, but the full project was never completed.  Raytheon built a successful 3-car test track at their headquarters in Marlborough, Massachusetts and was working on how to scale this up when a change in Raytheon’s finances caused the PRT unit suddenly to be canceled.

One problem was that the car location was calculated not by GPS (which despite a 1994 Federal Communications Commission  ruling wasn’t fully in the public domain yet) but by the number of wheel rotations; however, curves on the track caused uneven wheel wear, meaning the accuracy of the rotation count wasn’t sufficient to run the cars on the very tight few-seconds headways that were called for.  The RTA had assigned its entire R&D budget to the PRT project in exchange for future royalties from applications elsewhere.  After Raytheon unilaterally bowed out, no transit agency in the U.S. is likely to ever take such a risk.

The City of SeaTac was studying a PRT application around the time of the Rosemont project; the  concept was to replace the many street-clogging shuttle vans that serve airport hotels and parking facilities, with a PRT system that would deliver passengers directly to their destinations.  SeaTac, having selected the same Raytheon technology, decided to wait on the outcome of the Rosemont project.  The failure of Rosemont meant the failure of the SeaTac project.

Where is PRT Heading in the U.S?

Without federal or transit agency funding it may be very difficult to initiate other PRT in the U.S. However, interest remains strong in other parts of the world today including India, Mexico and Sweden.  In the US conversations are under way for a couple of new applications. It’s clear that with the right funding and the right contexts, many applications are possible.  It uses electricity, which has the potential at least of being a “green” or renewable energy source.  The small cars offer the privacy of a private vehicle; the offline stations offer speed of travel.  The small, light guideways mean that the PRT system can run inside major buildings such as sports stadiums, shopping malls, hotels and the like. In PRT’s heyday the vision was that it would be as ubiquitous as Velcro.

And yet its original conceptualization of providing an alternative to suburban car travel is called into question in at least two ways:

  1. The comparatively high cost of an elevated guideway, (as opposed to operating at grade) coupled with the relatively low capacity in terms of passengers per hour, mean that the cost per passenger mile may be high compared with other suburban choices.
  2. Providing a new transit system to specifically serve suburbs is counter to the very apparent need facing us in the United States, for more compact communities where carbon footprints will be lower. The always – skeptical  James Howard Kunstler disagrees with PRT: “If we’re going to replace the car why do it with something that’s not only like the car, but not really as good as the car? It just seems crazy.”

In reality, PRT’s most cost-effective and productive uses may be not for suburban trips but as a connector from remote parking lots or heavy rail stations, to major public facilities such as sports stadiums, hotel complexes, major medical facilities, convention centers, airports and shopping malls.

Perhaps the future of suburban (and urban) travel lies with driverless cars managed by Uber, Lyft and similar operations. Or, given the massive changes in transportation of the past 120 years, perhaps with technologies we cannot yet imagine.

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