Hundreds of drivers from New York, California and Washington, D.C., are set to participate in the most extensive field test to date for hydrogen-powered electric cars, Newsday reports.For 33 months the test drivers will take turns in a fleet of about 100 Chevrolet Equinoxes with a hydrogen fuel cell powering an electric motor to propel the car.The Equinoxes' fuel cells make electricity from oxygen in the air and hydrogen stored on board. The only by-products are heat and water vapor.Though cynics wonder whether some carmakers' talk about fuel cells is mostly to deflect pressure for higher-mileage gasoline-powered vehicles, those involved in the research seem genuinely enthusiastic. Honda, for example, has 15 experimental fuel-cell cars on the road, mostly in the United States. It is scheduled Nov. 14 to unveil a successor to them at the Los Angeles auto show. According to Newsday, fuel economy is twice that of a conventional Equinox, but hydrogen costs twice as much so it's a wash economically.