With a top speed of 100 mph, you won’t be breaking the barrier of sound, but with gas at $3.14 per gallon, you won’t be breaking the bank, either. Cars powered by hydrogen fuel cells are the latest frontier of clean energy. These cars are road-ready, with an ability to travel almost 250 miles on a full tank. The U.S. Postal Service uses a General Motors’ HydroGen3 to deliver mail in D.C., and the District Department of Transportation uses one in its Urban Forestry Administration program. The design could stand to be cooler, but this is not your mother’s minivan: It can go from 0 to 60 in less than 10 seconds, burning liquid nitrogen at -423 degrees, emitting only pure water vapor. If you think that sounds cool, imagine what it’d be like to make your own. Joining the frontlines of fuel-cell technology are high-school kids who want to take a crack at building a hydrogen-powered engine. Teams from 16 high schools will compete in the Model Hydrogen Fuel Cell Car Challenge, in conjunction with the 2006 Department of Energy National Science Bowl. Two separate competitions, including “King of the Hill,” which requires the model cars to make it up a steep incline, pit the teams’ model cars against one another. A General Motors engineer will be present at the event, offering test drives of the HydroGen3. The races begin at 2:45 p.m. at the 4-H Conference Center, 7100 Connecticut Ave., Chevy Chase. Free. (301) 961-2801. (Megan Maher)