The June 2024 issue of IEEE Spectrum is here!

Close bar

Made-to-Measure Mass Transit

Driverless cars aim to give each passenger a customized ride

4 min read

A snaking array of steel pillars outside the newly renovated Terminal 5 at London's Heathrow Airport will, by the end of next year, hold up a guideway upon which little automated electric vehicles will shuttle passengers and airport workers back and forth between the terminal and a distant parking lot. In doing so, the pillars will also be supporting a transportation movement decades in the making.

The project--dubbed ULTra (Ultra Light Transport) and designed and built by Advanced Transport Systems, of Bristol, England--is but one example of a mode of quasi-public transportation known as personal rapid transit, or PRT. According to PRT purists--including the board of the Advanced Transit Association, which advocates the use of technology to solve transportation problems--this label can be applied to transit systems that have all the following characteristics: fully automated vehicles that run on a reserved guideway; small vehicles that can, like taxis, provide exclusive use for small groups or even a single passenger; nonstop service using the most direct route available; off-line way stations; and on-demand access to vehicles instead of fixed schedules [see photo, "At Your Service"].

As with ice cream, the basic ingredients that PRT systems have in common impose few limits on variety. When ULTra is completed in late 2008, it will comprise 3.9 kilometers of paths populated with battery-powered, four-seat jitneys capable of speeds up to 40 kilometers per hour and able to follow each other with a 6-second separation between one car's tail and the next one's front bumper. ULTra's cars will run on rubber tires; other proposed systems will anchor the cars on rails above the guideways or suspend them from the dedicated paths.

Because this will be the first true PRT system to go into passenger service, the ULTra project is a test case for whether all the claims made by PRT proponents are true. Proponents maintain that PRT can be an important complement to existing mass-transit systems such as light rail, commuter trains, and buses. PRT advocates also predict that personal rapid transit systems will entice people to drive less, reducing the congestion, energy consumption, and environmental impact from passenger car traffic.

If ULTra can be completed on time, on budget, and operate as designed close to 100 percent of the time, it could represent a tipping point. Once Heathrow has set the example, other municipalities might jump on the bandwagon. ”There's a long, long line of cities, and they're all really keen on being second,” says Martin Lowson, Advanced Transport's CEO.

IMAGE:Advanced Transport Systems

AT YOUR SERVICE:Advanced Transport’s four-seat jitneys will provide private, nonstop, on-demand service along exclusive guideways.

But to this point, a host of variations on the theme have always fallen short when transit authorities have looked to expand their operations. For example, the city of Irvine, Calif., reported earlier this year that PRT is no longer under consideration for a transit extension that would serve a new park being built on the grounds of a shuttered U.S. Navy air base.

Some observers say that PRT's inability to gain any footing is purely political. ”The rail lobby has exhibited a lot of influence over these types of decisions,” says Robert Hendershot, who runs a PRT-like system that connects scattered parts of the University of West Virginia's campus with the city of Morgantown's central business district. ”The technology has really proven itself,” he insists, adding that, ”Honestly, I thought the tipping point would have occurred 10 or 15 years ago.” But Morgantown's 30 year track record doesn't sway decision makers because it isn't considered a true PRT system. It features 20-passenger cars and frequently operates on a scheduled, station-to-station basis during peak hours rather than on demand.

Also getting in the way is the memory of one or two past PRT projects that failed spectacularly and others that went away quietly after funds dried up. One oft-cited example is PRT2000, a Raytheon-backed transit system that was to be installed just outside Chicago during the 1990s. Raytheon terminated the project when the company discovered that changes from the original design conceived by University of Minnesota engineering professor J. Edward Anderson had raised the construction costs to nearly US $30 million per kilometer. (The rights to Anderson's design, which subsequently reverted to the university, were later sold to a Fridley, Minn., start-up called Taxi2000.)

Asked about these failures and what sets Advanced Transport's effort apart, Martin Lowson, the company's CEO, gave several reasons for optimism. ”Early attempts happened in the 1960s and 1970s,” he says. ”Technology has advanced a long way since then--not only in capability but in cost. Components that would have cost tens of thousands of dollars 20 years ago you can now get for less than a thousand.” Still, the company's mantra has been ”no more technology than necessary.” Lowson says Advanced Transport takes pride in the fact that ULTra will use mostly off-the-shelf equipment, including a 48-volt lead-acid battery for propulsion power. It will also have an anticollision system modeled on the one used by railways for decades, in which the cars communicate their positions on the track via inductive loops in the tracks instead of a more expensive wireless link. The results, he says, are lower start-up and operational costs as well as greater reliability. He notes, for example, that in two years of tests at the company's 1-kilometer track in Cardiff, Wales, the system hasn't failed.

Critics, however, remain unconvinced. For this limited application, covering one part of Heathrow, personal rapid transit might work, says Vukan R. Vuchic, a professor of transportation engineering at the University of Pennsylvania, in Philadelphia. But he doubts that the system will be scalable--not even to the extent that it will be able to take over from shuttle buses the entire task of ferrying people across all of the airport's grounds. ”I don't see what kind of function personal rapid transit will serve, because it combines the negative features of cars and subways: expensive guideways [for subways] and low capacity [of cars].”

Mike Lester, chief operating officer at Taxi2000, explains that PRT was never meant to replace trains and buses but to extend their reaches in ways that are less expensive and more environmentally friendly. ”You'll never hear me say that we shouldn't have light rail or subways,” Lester insists. He and Advanced Transport's Lowson say that one of the tough parts of waking people up to the benefits of PRT has been managing expectations. ”There are a lot of people who are skeptical about it, which is an entirely reasonable point of view to take when it comes to new technology,” says Lowson. ”We have a low-speed system with modest capacity, and we're very confident that we can do an effective job delivering that service in a way that is reliable and ranks high in terms of passenger service.”

This article is for IEEE members only. Join IEEE to access our full archive.

Join the world’s largest professional organization devoted to engineering and applied sciences and get access to all of Spectrum’s articles, podcasts, and special reports. Learn more →

If you're already an IEEE member, please sign in to continue reading.

Membership includes:

  • Get unlimited access to IEEE Spectrum content
  • Follow your favorite topics to create a personalized feed of IEEE Spectrum content
  • Save Spectrum articles to read later
  • Network with other technology professionals
  • Establish a professional profile
  • Create a group to share and collaborate on projects
  • Discover IEEE events and activities
  • Join and participate in discussions