Calling all cars, while quietly scanning one car

Call it the dash-top computer.

You'll find it in any local police cruiser -and soon in the hands of foot and bicycle officers, too.

The mobile data terminal is like an Internet chat room on the road.

But its mission is much more critical.

It helps officers respond more quickly to emergencies, helps keep them safe in traffic stops and on patrol, and helps them nab more criminals.

Atlantic City, N.J., introduced the first in-car police computers in the late 1970s to speed response times in emergencies.

Over traditional police VHF radios, one frequency can handle only one conversation at a time.

So checking a license plate would tie up a dispatcher as well as an officer (and possibly a partner in the patrol car) for several minutes.

But with mobile computers connected to a network, an almost unlimited amount of information can flow simultaneously.

A dispatcher can send out several cars, and officers can acknowledge the calls simultaneously. Meanwhile, one of the patrol officers can check a suspect's record from the front seat of the car.

Say a policeman pulls you over. By the time he gets to your window to ask for your license, he could call you by name.

He already knows your driving record, where you live, whether the car is yours or has been reported stolen, whether anyone has a warrant for your arrest, and whether you're likely to be armed.

When the cop punches in your license number, the mobile data terminal beams a signal to the nearest of several antennas atop local buildings. The base transmitter there uses two frequencies to communicate with the police cruiser: one for sending and one for receiving.

A radio-network controller makes sure at least one base site has contact with every police unit.

The network controllers, in turn, are connected to the dispatch center, where 911 calls arrive and radio dispatchers work.

The dispatch center is connected to a statewide police information center with access to information from the state motor-vehicle department, the National Crime Information Center in Washington, and the National Law Enforcement Telecommunications System, a clearinghouse for driver and vehicle information from other states.

Any black marks from any of those sources show up on the computer screen in the police car within seconds - and without tying up a dispatcher to do the research.

Another advantage: Since electronic messages never squawk over a loudspeaker, a wanted fugitive doesn't know he's busted, and is less likely to make a run for it.

Police departments in metro areas are looking at expanding the technology to hand-held devices, so officers aren't tied to their cars.