Golf carts on sticks

By Michael Fraase

Tuesday, 26 August 2003 06:46PM CST

Section: Sustainability

The future of sustainable motorized transportation is an enclosed driverless golf-cart-on-a-stick. Known by lots of names—Skyweb Express, Taxi 2000, MicroRail, Higherway, or Skycab—they’re all trade monikers for Personal Rapid Transit (PRT), a system for moving people in a manner similar to the way networked computers move bits of information around the Internet.

The PRT cars look like Jetsonesque enclosed golf carts that run on a narrow elevated guideway that very much resembles a life-sized slot-car track. Only the body of the car can be seen above the guideway. Underneath is a short post connected to an induction motor and a set of four tires on wheels that ride in the semi-enclosed guideway.

The guideway forms a network throughout a metropolitan area. Like the Internet, the PRT network itself is quite unintelligent; there’s absolutely no intelligence embedded within the PRT cars or the guideway. All intelligence, again like the Internet, is found at the edges of the network; in the case of PRT, the intelligence resides in the computers that control the cars. The result is maddeningly simple: PRT moves people the same way the Internet moves data.

Personal Rapid Transit (PRT) car
Taxi 2000 Personal Rapid Transit (PRT) car.

Because the cars are simply constructed and lightweight, the guideways can be small, cheap, and cause minimal construction disruption; guideways can be built at an exceptionally low cost of between US$5 million and US$10 million per mile. Best of all, cars move only when they’re transporting humans (or cargo) or routing to demand, and even then the entire system is up to four times more energy efficient than the equivalent number of automobiles. The system is exceptionally quiet and there are no emissions from the PRT cars themselves. The intelligence of the computers controlling the PRT cars ensures that network usage is optimized and car availability is nearly on-demand. There are no traffic jams, no gridlock, and no accidents because merging and exiting to and from off-line stations is all controlled automatically

The projected user experience offers some interesting advantages over other transit options. The PRT ride is completely private—although stations and individual cars will likely be monitored for security and safety—and non-stop. A rider merely finds a station, selects a destination, and enters the car. Route maps and schedule tables are unnecessary; the entire operation is based upon on-demand principles. Once the destination is selected, the computer controller determines the fastest route based on the appropriate factors.

Personal Rapid Transit (PRT) station
Offline Personal Rapid Transit (PRT) station.

Unlike competing transit systems, PRT is a completely modular system. Adding new stations doesn’t add to the existing ride-times and station construction doesn’t require the system to be taken off-line. Adding more stations simply makes the system even more useful.

The benefit to individual transit users is clearly apparent. But what about benefits to the community?

The elevated guideway used by PRT are 3-feet x 3-feet square and can be run down streets, alleys, and even through buildings. As a result, land use requirements are significantly lower, and land previously dedicated to automobile infrastructure (more than half of the land available in city centers)—parking lots, parking garages, bypasses, gas stations, even interstate corridors in metropolitan areas—can be reclaimed for other uses. A single PRT guideway’s capacity is roughly the same as that of a four-lane highway.

One of the leading PRT developers, Minneapolis-based Taxi 2000, estimates its system will cost US$10 million per mile compared to about US$300 million per mile for a bi-directional subway. “For the same cost as a narrow four-mile strip of subway with five stations, Taxi 2000 would provide 170 stations in a 5.5-mile-by-8.0-mile network with practically all of the area within a one-quarter-mile walk.”

A University of Washington study estimates the cost of building a metropolitan area PRT system are even lower at about US$5.5 million per mile. That’s a bargain in comparison to freeways and light rail construction, costing US$20 million US$70 million per mile, respectively.

In most cities today, only about 3% of travel is by traditional bus and rail transit systems. Because of inefficiencies built into these traditional transit systems, about 60% of their operating expenses must be subsidized. PRT will likely require no operational subsidy. “Operating and maintenance costs for Taxi 2000 will be about 8 cents per passenger-mile compared to 27 cents for the subway, 29 cents for the bus, and 42 cents for the streetcar (light rail),” says Taxi 2000. A commercial endeavor should be able to operate its PRT system in most metropolitan areas without any sort of operational subsidy while generating a fair profit for its owners. Imagine that.

Note: a condensed version of this article was published in the September / October issue of Utne magazine ($$).

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