Just seven months after starting production of conventional Civics at its new Honda Manufacturing of Indiana plant, the automaker has rolled the first of its ultra-clean Civic GX models off the line in Greensburg. Previously assembled at the firm's East Liberty, Ohio, facility and powered by compressed natural gas, the GX is the only CNG-fired car made in America by a major auto manufacturer -- and the only one to be sold in all 50 states. Winner of the American Council for Energy-Efficient Economy's "America's Greenest Car" award for five years running, the GX is 90 percent cleaner at the tailpipe than the average gasoline-powered car, sufficient to qualify for ILEV (Inherently Low Emission Vehicle) status with the EPA. It's powered by a specially modified version of the Civic's 1.8-liter four-cylinder i-VTEC engine that features a loftier 12.5:1 compression ratio to take full advantage of CNG's inherently higher octane rating (130 RON). Developing 113 horses and backed by a five-speed automatic transmission, it returns 24 mpg in the city and 36 mph on the highway. While the GX does suffer a certain degree of range limitation that impacts all CNG-powered vehicles, it still manages to return a very usable 220 miles GGE (Gasoline Gallon Equivalent) on a single fill of its 8.0-gallon fuel tank. And it qualifies for a $4,000 Federal tax credit as an alternative fuel vehicle.