Japanese automakers are leaving the rest of the world behind in developing and applying green technology in their vehicles. In the latest study from the Union of Concerned Scientists (UCS), Honda, Toyota and Nissan rank 1-2-3 for reducing global-warming emissions and smog-forming pollution. No other carmaker even comes close, and the results belie advertising claims made by several companies.

“There is a huge gap between the cleanest and dirtiest automakers,” says Don MacKenzie of UCS, the study’s lead researcher. “The winners are using clean technology across their entire fleets.  The losers are installing it piecemeal or not at all.” 

MacKenzie analyzed the cleanliness of 10 vehicle classes produced by eight automakers, which comprise 96 percent of the U.S. market. A few clean vehicles didn’t affect a manufacturer’s overall score. Instead, the study aimed to account for average per-mile emissions across a carmaker’s entire product line. Hybrids help an automaker in the rankings, but only if they make good use of the technology in many products.

Hyundai-Kia, Volkswagen, Ford and General Motors trailed the Japanese manufacturers. DaimlerChrysler came in dead last; its vehicles emit 70 percent more smog-forming pollutants and 30 percent more greenhouse gasses per mile than do Honda’s.