Smile, You’re on Photo Radar!

By Ed Martinez

Published in the Winter 2009 issue of MyTekLife Magazine

It seems as though they’re everywhere these days—photo radar units. Chances are, you’ve probably seen one along your local highways or traffic stops. Photo radar units have been the center of much controversy ever since city and county governments deployed them across the U.S. Much of the debate is over whether they’re being used to generate revenue or to promote public safety.

But how exactly do they work? The technology behind them is extensive, but for the most part, it’s also straightforward. Let’s look at the two most commonly used photo radar devices, intersection speed cameras and highway speed cameras.

Intersection speed cameras are responsible for recording red light violations. They use induction-loop triggers that are positioned under the asphalt, near the stop line. The trigger connects to an electrical power source and meter, which generates a magnetic field. The meter monitors the total inductance level of the circuit. When a significant change is made, a computer catches the change and determines that a vehicle has crossed over the loop. If a vehicle sets off the trigger when the light’s status is red, the computer snaps two pictures with 35-mm cameras—one of the vehicle at the edge of the intersection, and the other showing the vehicle in the middle of the intersection.

In addition, intersection cameras have been programmed to register the speed of vehicles as they cross the intersection. If a vehicle is traveling faster than the posted speed limit, the cameras activate and record the violation.

On the highway, you will find cameras similar to those in place at intersections, although the technology used in the highway speed cameras is not as complicated. With built-in radar units similar to those used by law enforcement personnel, the cameras detect the speed of a traveling vehicle and snap pictures if the vehicle has exceeded the maximum speed limit. Three photos are taken when a violation occurs. The cameras snap a picture of the driver, front view of the vehicle and the back of the vehicle—with a clear view of the license plate. Most law enforcement agencies allow up to 10 miles per hour over the posted limit before a violation is considered.

Hundreds of pictures taken by photo radar units are examined daily, matching the drivers with their driver’s license photos on file. When a match is made, a citation is issued and mailed to the registered owner of the vehicle.

Whether the debate will continue to stir controversy is something to keep a close eye on. The reality is that the photo radar units are here now, and you should be aware of them when driving. If you do happen to find yourself in the unfortunate situation of being photographed by one, don’t forget to smile!