It's a hot and smoggy day in Washington, DC, and things aren't going well for Les Goldman, a longtime energy lobbyist whose latest project is a new kind of car that is supposed to slash gasoline consumption and reduce greenhouse-gas emissions. We're outside his office, a block from the White House and a quick trip down Pennsylvania Avenue from Capitol Hill. And Goldman is sweating at the back of the "plug-in" hybrid that I'm supposed to test-drive, checking electrical connections and trying to figure out why it isn't working.

The car is a modified Toyota Prius with an extra battery installed in the spare-tire compartment. Conventional hybrids like the Prius run on an electric motor part of the time, but the electricity they use is generated by a gasoline engine and by capturing energy from braking. In the plug-in version of the car, the extra battery can be recharged from an electrical outlet. The battery stores about 40 miles' worth of electricity; if it's depleted, the car reverts to conventional hybrid mode.