That would be vehicles powered by CNG (compressed natural gas).
It appears that the Iranians have a much better energy plan than us.
Houston, Dallas, Los Angeles and San Francisco are the only major metros with aggressive CNG programs for building CNG Filling Stations. Even my little town is getting ready to open its fouth CNG Filling Station(as well as one of the few cities wired with Fiber Optics).
Talk of energy independence is cheap. Action is what we need!