READING, Pa. (AP) — The federal government says its periodic roadside survey on motorists' drinking and drug-taking habits is anonymous and entirely voluntary.

But the National Roadside Survey of Alcohol and Drugged Driving is being criticized by some motorists and civil liberties groups who say the government's methods are intrusive and even unconstitutional.

One Pennsylvania motorist has filed a federal lawsuit over the survey, saying his rights were violated when a government contractor forced him into a parking lot where he was questioned about his driving habits and asked to provide a saliva sample. Some police departments have refused to partner on the survey or regretted their decision to do so following public outcry.

U.S. transportation officials call the $7.9 million survey a vital tool for monitoring the safety of America's roadways.

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