The study examined average fuel economy and emissions and used that to estimate the amount of greenhouse gases each car and truck fleet produced.
"By implementing gas saving technologies and reducing emissions below required levels, Honda produced the vehicles with the best environmental performance in today's market," according to UCS.
Since 1988, Honda has built most of its Accords and Civics to meet California's LEV standard, which is 57 percent more stringent than the EPA's current standard. At the same time, Honda leads other automakers in fuel efficiency with cars that average an industry-best 31.8 miles per gallon.
While the study was the first of its kind by UCS, the group found that pollution had been rising. Strong sales of light trucks, which count for about half of all new vehicle sales in the U.S., account for pushing overall fuel economy down to 23.8 miles per gallon, the lowest levels in 20 years.
Honda has been recognized by the Sierra Club, AGEEE's Green Book and now the UCS -- environmental groups with no ties to automakers -- in setting an example for producing cleaner vehicles on a large consumer scale. In other words, Honda continues to demonstrate, not just promise, its commitment to clean air.