Prince George's County police officers are no dummies. But motorists may have to take a closer look to make sure.

The reason is that half a dozen new traffic officers are taking to the roads: They are diligent, hard-working, loyal, but a little stiff. In fact, they're wooden.

Known collectively as Officer Doppler, the dummies (police prefer the term mannequins) started appearing in police cruisers across the county last week in an effort to deter speeding.

Named after the 19th century physicist Christian Johann Doppler, who discovered the principle on which radar was developed, the mannequins will "monitor" areas where excessive speeding takes place or numerous accidents occur. Police hope they have a different type of Doppler Effect.

"Whenever you see a police car, most people slow down, regardless of who is inside," said Sgt. David Dennison, who is part of the county's Traffic Safety Unit. "That's the effect we're looking for. We're looking to slow speeds to prevent accidents."

Primped and propped up for the media behind the wheel of an extra police cruiser at the District 5 Station in Clinton by his partner, Cpl. John Daley, the stoic Doppler, donated by JC Penney Co., looked ready for action. Or inaction, depending on how you look at it. According to the company, the mannequins cost a pretty penny, about $1,000 each.

He has perfectly coiffed (albeit rock hard) jet-black hair, a pair of sporty black sunglasses ("He has no eyes," Daley explained) and a neatly pressed uniform shirt ("It's mine. I had an extra," Daley said sheepishly).

While driving by, police insist, motorists will not be able to tell the difference between Doppler and a real officer. To further confound speeders, police will alternate Doppler and real officers with radar-equipped cars.

"One day Officer Doppler will be out there on the road and the next day a real police officer will be out there checking speeds," Dennison said. "People may not find out which is which until it's too late."

The ruse has been used by police forces across the nation, including Rockville's, with varied success. While police officials said they don't believe Doppler will stop speeders or have a long-term effect, he "will put a little doubt into their minds and they will slow down," Daley said.

"The less time they are speeding, the less likely they or anyone will get into an accident."

Doppler is part of an effort by Maryland officials to curb speeding.

In a recent crackdown by Maryland State Police, more than 52,000 speeding tickets were handed out, a fifth of those for speeds that approached 80 miles an hour.

Daley, who sees Doppler as more than just a neat torso, has taken quite a ribbing from his collegues.

"They keep asking me stuff like: 'Who's smarter, you or the dummy?' " said Daley, who will check on Doppler periodically during its shift. "But I just tell them the reason we have the dummy doing this is because they weren't smart enough themselves."