United Press International - upi.com

DUBENDORF, Switzerland, Dec. 19 (UPI) -- A Swiss study indicates motorcycles collectively emit 16 times more hydrocarbons and three times more carbon monoxide than do cars.

The study by Ana-Marija Vasic and Martin Weilenmann of the Swiss Federal Laboratories for Materials Testing and Research found both two- and four-cycle motorcycle engines emit significantly more pollutants than automobile engines.

They said of particular worry were the high levels of hydrocarbons emitted by Japanese, German and Italian two-wheelers, since some hydrocarbons have been linked to global warming or are suspected of being carcinogenic.

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Since motorcycles aren't a primary means of transport in most developed nations, the authors said, "The importance of (motorcycle) emissions has been underestimated in legislation, giving manufacturers little motivation to improve after-treatment systems."

For example, until recently U.S. emission standards for highway motorcycles hadn't been updated in 25 years, despite the fact such vehicles produce more harmful exhaust emissions per mile than cars or even large sports utility vehicles.

The study is to be published in the Jan. 1 issue of the American Chemical Society's journal Environmental Science & Technology.