The Westchester County (N.Y.) Police Department uses a ghost car, a cruiser that has no roof lights and whose markings can be seen only at close range. Their "low-profile" police vehicle, in the background, does not have the traditional light bar on top. (Photo by Westchester County (N.Y.) Police)

Speeders, beware: That innocent-looking Chevrolet Camaro, Ford Fusion or SUV you're about to blow past just might be the law.

In their effort to reduce speeding - a factor in nearly one-third of all highway deaths - state and local police agencies around the USA increasingly are using unmarked patrol cars, sports cars and even "ghost" cruisers with obscured markings.

"This is not about being sneaky," says Fargo, N.D., Police Chief Keith Ternes, whose department recently began using unmarked vehicles. "This is about trying to change people's habits and having them pay attention to their driving even when they don't think a police officer is watching."

Police departments say the move is necessary because some of the nation's worst, habitual speeders constantly spot marked cars in time to avoid hefty fines that could change their behavior.

It's a deadly cycle: Speeding contributed to 31% of all fatal crashes in 2008 - 11,674 lives - at a cost of $40.4 billion, says the National Highway Traffic Safety Administration. Among police agencies making it harder to spot traffic enforcers:

James Shell, 55, of South Bend, Ind., got a ticket after he roared past a gray Mustang at 80 mph in a 60-mph zone. "After I got around it, in the rearview mirror I could see him put on his Smokey Bear hat," says Shell, 55, a Labor Department investigator. "That's when he hit his lights. I was like, they now use souped-up Mustangs?" Shell's inattentiveness cost him about $120, but he learned a lesson. "Most definitely, it had an impact," he says. "Since that happened to me, I said never again. It made me slow down."