Though bicycles are the most widely used vehicles in the world, as well as the most energy efficient, they still play a minor role in the U.S. transportation system. The problem, according to many observers, relates to infrastructure. "Technical advances are leading to faster and faster bikes, but we don't have the facilities to accommodate them," says Milnor Senior, head of Bicycle Transportation Systems, Inc. in Denver. Safety is a related concern. "In so many places, there's too much hazard, or perceived hazard, for cyclists to get out into traffic without putting their lives at risk," notes Gerry Hawkes, president of Bike Track, Inc. in Woodstock, Vt.

Both Senior and Hawkes hope to change this situation with their plans for new kinds of bike conveyances. Senior's scheme, "TransGlide 2000," consists of a four-lane "transportation corridor," placed either on the ground or elevated above roadways. The system, he says, is intended to move people through an urban area with the "highest average speed and lowest cost."