This three-wheeled car runs on gas fumes. An entry for the Progressive Automotive X Prize, a contest for the most fuel-efficient car, it was on display at the New York International Auto Show March 18 Mark Lennihan/ap

New York - Drivers often joke their car "is running on fumes," when the tank gets low. Well, how about an engine that actually gets its energy from gasoline fumes?

Or, tired of looking for parking space? Well, someone has dreamed up an all-electric car so thin it can compete with motorcycles for the gaps between SUVs.

And no need to fill up on expensive gasoline anymore – one would-be Henry Ford wants to build an engine that runs on compressed air, the stuff that fills your tires. Naturally, it's called the Air Car.

All of these ideas – some with actual tires on the ground – are entered for the Progressive Automotive X Prize, an international competition that will award $10 million to the first team that can build and bring to market a car that gets the equivalent of 100 miles per gallon. So far, no major auto company has said it'll compete, although some have said they are curious and might kick a few tires when no one is looking.

There will be a contest, scheduled to begin September next year, in which these ambitious prototypes will be driven about like regular cars. And since Americans like to race – or at least go to NASCAR events – these decidedly non-Detroit vehicles will hold a race of their own.

Last Thursday, the X Prize Foundation rolled out some of the contestants at the New York International Auto Show, an event where "concept cars" usually just mean futuristic styling, or technology that won't be ready for the public to use until colonies are established on the moon.

"We need a car that is not just a concept but can be made in mass quantities at a reasonable cost for the average American," says Jack Hidary, chairman of the Coalition Advocating for Smart Transportation and a donor to the X Prize's new effort. "Unfortunately, Detroit has not stepped up to the plate, they have fought CAFE [Corporate Average Fuel Economy] standards every step of the way."

But some automakers say the competition is passé. Volkswagen has chosen not to participate.

"In 2001, we put a European Lupo3L hypereconomy car through the now-archaic EPA testing and got 80 miles per gallon in the city and 100 on the highway," says Keith Price, the public relations manager. "So in terms of the X Prize, we wish them well but from our perspective, we've been there, done that."

The Lupo is no longer in production.

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