Electronic traffic law enforcement involves the use of technology to enforce traffic laws. Police officers have been using conventional radar guns for years to detect speeding drivers. More recently, laser speed guns have been developed that more accurately clock the speed of moving vehicles. Red light cameras detect vehicles that run red lights at intersections.
Conventional Radar Guns
Police traffic radar uses one stationary antenna that points in one direction. A microwave beam is transmitted on a specific frequency. A vehicle that is intercepted by the beam reflects microwave energy to the antenna. A digital readout tells how fast the vehicle was approaching the radar or receding from it.
Police traffic radar does not tell the police officer which object is being measured or the direction of the vehicle. Radio wave or microwave interference can produce an incorrect reading on the radar unit's screen. Such interference can come from cellular telephones, two-way radios, mercury vapor lights, and high-tension power lines. Mechanical interference from another moving object can also produce an inaccurate radar reading. Some experts believe that about one-quarter of all radar-based speeding tickets are issued in error.
Laser Speed Guns
Laser speed guns use concentrated light. A laser gun measures the time it takes a burst of infrared light to reach a car, bounce off the car, and return to the starting point. By multiplying this time by the speed of light, the laser gun determines how far away the object is. Laser guns can take hundreds of samples in less than half a second; they are extremely accurate.
Red Light Cameras
Red light cameras are being used in over 200 cities throughout the nation, according to the Insurance Institute for Highway Safety. An electronic camera placed at an intersection detects when a vehicle has gone through a red light. A trigger mechanism causes a picture to be taken of the vehicle's license plate number. Depending on the law in the state, the driver or vehicle owner is sent a warning letter or mailed a ticket. In some states, automated enforcement tickets are not recorded on a driver's record and do not result in points. Similar cameras can be used to detect speeding, failing to pay a toll, and ignoring railroad-crossing signals. There is vocal opposition to red light cameras, and the use of such cameras has been stopped in several states.
Reduction in Accidents and Red Light Violations
Some studies have found a significant reduction in injury crashes where red light cameras are used. The use of such cameras has also been shown to decrease the number of red light violations by over 40 percent.
Copyright 2009 LexisNexis, a division of Reed Elsevier Inc.
