Some challenges personal transit systems face

The transportation model that Rosemont, Ill., is considering is a fleet of small, modular, computer-driven vehicles (see photo page 11), which seat up to four passengers. Designed by Raytheon Systems Co. based in Lexington, Mass., the vehicles operate on a narrow elevated track called a "guideway."

At each station, there's a ticket-vending machine that resembles an ATM, with a map of the route. Passengers would pay a fare by cash or credit card, and touch the point of destination on the map. The machine dispenses a ticket with a magnetic strip and destination encoded. The ticket is run through a slot on the vehicle, which informs the computer of the destination. All stations are off line, which allows each vehicle to travel non-stop from origin to destination.

The wait for a four-person vehicle is 3 minutes at most. Sounds like a car.

In a 1996 Urban Transport International issue Vukan Vuchic calls it an "expensive version of the private car."

"Private cars are ideal vehicles in sprawling residential suburbs, but inefficient in high-density central urban areas," he says. "Suppose a PRT [personal rapid transit] system has a station near a large office building.... Eighty people come from the building to travel to different points on the PRT network.... The PRT system should be capable of providing 50 vehicles in a few minutes. That can be done only if a large number of vehicles cruise empty - an expensive operation."