LIDAR: The Speed Enforcement Weapon of Choice

It's as easy as playing a video game at the local arcade; acquire target … steady, aim, shoot! But this is no game. In the world of traffic safety, when officers set out to work on catching drivers who race through crowded city streets, they want a tool in their arsenal that will accurately capture the speed data of these traffic violators. The weapon of choice in this game of cat and mouse is here: lidar.

Lidar (light detection and ranging) has become a popular tool with officers for speed enforcement, especially in congested traffic conditions. Unlike its brother, radar, the more widely recognized speed measurement tool, lidar allows for very specific target acquisition when attempting to determine the speed of a particular vehicle on a crowded roadway.

As lidar continues to make gains in popularity, a decline in radar sales has become noticeable. Carl Fors of Texas-based Speed Measurement Laboratories Inc., an expert in the field of development and evaluation of speed detection tools, reports laser gun sales now make up 30 percent of the speed enforcement electronics market, substantially higher than the 10 percent lasers had in 2004.

But make no mistake, lidar should not be purchased as a replacement for the current radar systems departments have in use. Instead, consider lidar as a new option for speed enforcement to enhance traffic safety efforts.

Something old, something new

Lidar uses a time-of-flight method for taking measurements to determine the target vehicle's speed. When a pulse is transmitted, the timer starts, and when that pulse hits its target and returns, the timer stops. The calculation of distance traveled over time is computed to determine speed. In many respects, this sort of technology may not sound like anything new. After all, we've been using radar in a similar fashion for years. The difference lies in the type and shape of the pulse being transmitted.

Radar shoots out a short, high-intensity burst of high-frequency radio waves in a cone-shaped pattern. Officers who have been through the painfully technical 40-hour Doppler radar training course know it will detect a variety of objects within that cone pattern, such as the closest target, the fastest moving target or the largest target. Officers are trained to differentiate and properly match targets down range to the radar readings they receive. Under most conditions, skilled users get good results with radar, and it is found to be most effective for open stretches of roadway. But for more congested areas, locking radar on a specific target is more difficult.

Lidar utilizes laser technology, allowing for superior target acquisition in high-volume traffic areas. According to Fors, "Laser systems are the most accurate means of providing traffic and speed analysis compared to other systems. A laser can pinpoint one vehicle in a group while radar can't. A laser beam is a mere 18 inches wide at 500 feet compared to a radar beam's width of some 150 feet." In congested traffic areas, an officer can very effectively use lidar to pick out a specific target, site it and read its speed without any concern for interference from other close-by targets.

This small beam width has another added benefit — it cannot be detected until after a speed measurement is already made. Testing of the most advanced detectors has shown that when officers aim properly (at the vehicle's front license plate instead of the windshield where the detector usually sits), the signal often goes undetected.

Lidar signals can be legally jammed, however. While radar jammers have been declared illegal by the FCC and cannot be lawfully produced in the United States, there are no laws prohibiting jamming police laser guns. Certain states, including California, Utah and Minnesota, have specific state laws banning the use and sale of laser jammers, though.