Honda’s vehicle product line is the least-polluting on sale in the United States market, while the DaimlerChrysler line comes bottom of a list of manufacturers selling environmentally friendly cars, a survey by the Union of Concerned Scientists said, according to Reuters. Reuters said the UCS survey, released Dec. 4, analyzed the environmental performance of the six largest vehicle makers in the U.S. market who collectively sell nine out of every 10 vehicles. Toyota, Nissan, Ford, General Motors and DaimlerChrysler followed Honda, Reuters said. Ford was the only vehicle manufacturer to move up in the UCS survey and the group said Ford's environmental progress was due to company Chairman William Clay Ford, Reuters said. "Ford deserves credit for going beyond federal requirements to clean up smog-forming emissions from its trucks," Jason Mark, who oversaw the UCS survey, told Reuters. "Bill Ford has touted his green thumb, but until now only his speeches have merited a thumbs up," he said, the news agency added. According to Reuters, the UCS said Ford was on track to meet its pledge to boost the fuel economy of its sport utility vehicles by 25 percent from model year 2000 to 2005, but Ford's SUV gains were offset by fuel economy declines in the firm's other vehicles. Reuters said the UCS survey looked at the two main environmental problems related to vehicles – smog-forming pollution and carbon dioxide emissions that are linked to global warming. Vehicles sold by the six largest car makers account for 93 percent of all smog-forming pollution and 92 percent of all carbon dioxide emissions, Reuters said.