Your own personal monorail?

"I'm skeptical because we already have a potentially quite functional bus system that has been grossly underfunded for a long time," says Betsy Barnum, a Green Party activist. "If it were fully funded it would be a good transit system. I think it should be fully utilized before starting up another whole new system."

Ms. Barnum adds she is concerned about the potential visual impact of the overhead guideways.

"Visual impact is probably the most important problem we have to cross," Taxi 2000's Anderson says. "If it's going to be practical and safe it has to be out of the streets. Underground is too expensive so elevated is the only place you can put it. So we have to make the smallest, most attractive guideway we can."

The technology was initially proposed more than 30 years ago. Richard Nixon promoted PRT in the early 1970s during a time of increasing dissatisfaction with urban congestion.

His administration spearheaded a model project in Morgantown, W. Va., but what politicians ended up with was a sort of automated bus system, with huge cost overruns, that continues to serve Morgantown but tainted PRT for nearly 20 years.

Now because of growing challenges with urban transportation, the technology is back on the drawing board - and promising greater efficiency.

PRT's infrastructure makes it less expensive to build than other types of mass transit, proponents say.

"[It] can be installed for a cost between one-half and one-third of the cost of light rail," says Martin Lowson of Advanced Transport Systems, maker of the ULTra PRT system. Lowson estimates that it would cost one-tenth the expense of building a roadway to install PRT. His company has found people would be willing to pay $3 per fare.

In February, 71 percent of Welsh passengers who used public transportation said they'd pay more for PRT than buses, and 11 percent said they'd pay as much as they'd pay for a taxi.

Mr. Zimmerman, the Minneapolis councilman, says a test track in his city would cost $61 million; a 68-station, 31-mile system like he's proposing, $600 million. Construction is fast and operating costs are low because the system is automated, according to Skyweb.

[Clarification: However, engineers and transit experts have raised concerns about the costs of PRT. For example, a 2001 engineering study for the Cincinnati area projected costs six times what PRT proponents had estimated, in part because of the system's complexity and the need for greater physical support of the structure. Independent transit experts note other hurdles, including the high price of acquiring right of way.

But PRT advocates see a market for the technology.]

These systems appeal to people who already use, or would like to use, public transit, because they won't have to wait for vehicles and there won't be stops, says Tom Miler, president of the nonprofit group Citizens for PRT in Minneapolis.

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