The greenest car in America still runs on fossil fuel: Compressed Natural Gas (CNG).
 
Honda Civic Natural Gas Named 2012 Green Car of the Year

The all-new 2012 Honda Civic Natural Gas – the only factory-built, CNG-powered car produced in America – was named 2012 Green Car of the Year® at the Los Angeles Auto Show today. The award was presented to Honda by the editors of Green Car Journal representing a diverse panel of environmental experts and automotive enthusiasts who annually select a single vehicle for its outstanding environmental performance.

After the announcement the earth might have moved, but it would have been from hydraulic extraction. Who are these people that consider a fuel dependent on fracking to be the greenest choice? 

The Green Car of the Year® is presented annually by the Green Car Journal. In addition to the publication's editors, jurors include Carl Pope, chairman of the Sierra Club; Frances Beinecke, president of the Natural Resources Defense Council; Jean-Michel Cousteau, president of Ocean Futures Society; Matt Petersen, president of Global Green USA; Jay Leno, noted auto enthusiast and host of the "Tonight Show," as well as automotive icon Carroll Shelby.

Interestingly, Carl Pope was just forced out of the Sierra Club: 

The move reflects a broader debate among many of the nation’s environmental groups, which are finding it a challenge to raise money, motivate activists and build public support for core concerns like climate change in the face of high unemployment and hostility from Republicans in Congress and on the presidential campaign trail.
 
Membership rolls at the Sierra Club, one of the nation’s oldest and most prestigious environmental groups, have dropped sharply in the current economic downturn and the organization has undergone a sharp internal debate over priorities. Mr. Pope advocated partnerships with business and industry on a number of environmental projects, alienating some of group’s older donors and activists.

The Natural Gas Vehicle Association notes the advantages of CNG:

Replacing a typical older in-use vehicle with a new NGV provides the following reductions in exhaust emissions of:
 
Carbon monoxide (CO) by 70 percent – 90 percent
Non-methane organic gas (NMOG) by 50 – 75 percent
Nitrogen oxides (NOx) by 75 – 95 percent
Carbon dioxide (CO2) by 20 – 30 percent
 
Per unit of energy, natural gas contains less carbon than any other fossil fuel, and thus produces lower carbon dioxide (CO2) emissions per vehicle mile traveled. While NGVs do emit methane, another principle greenhouse gas, any increase in methane emissions is more than offset by a substantial reduction in CO2 emissions compared to other fuels. Recent analyses estimate that NGVs produce up to 20 – 30 percent less greenhouse gas emissions than comparable diesel and gasoline fueled vehicles.

The tailpipe exhaust in your neighborhood will be much cleaner, but Triple Pundit notes that there is significant exhaust when and where the natural gas is released through hydraulic fracturing: 

Greenhouse gas emissions are another problem caused by fracking. Natural gas is “composed largely from methane,” according to a Cornell University report released last spring. The report states that 3.6 percent to 7.9 percent of methane from shale gas production escapes to the air, and methane emissions from shale are at least 30 percent more than from conventional gas.
 
“Even small leakages of natural gas to the atmosphere have very large consequences,” Robert Howarth, an environmental biology professor at Cornell University, who worked on the methane report, said. “When the total emissions of greenhouse gases are considered … natural gas and coal from mountaintop removal probably have similar releases, and in fact natural gas may be worse in terms of consequences on global warming.”