A Snipe at Speedsters

Lidar offers pinpoint accuracy in nabbing speeding motorists.

by / March 9, 2007 0
If using radar to catch speeding motorists can be described as throwing a net over a wide area in hopes of catching something, then lidar is a rifle shot, pinpointing the intended quarry. But both have their places in law enforcement, and neither can replace the other.

Radar has been used for decades with more than adequate results, and lidar has come onto the scene in recent years as a viable companion to radar.

Radar -- short for radio detection and ranging -- sprays a web of high-frequency radio waves in a cone shape, finds an object, and gauges its speed. Radar uses electromagnetic waves, or radio waves, to locate moving or fixed objects. A radar beam used for tracking the speed of motor vehicles is typically 12 feet wide and 100 feet long.

It uses the Doppler principle, which measures frequency change. The radar transmits a microwave frequency that bounces off the vehicle and returns to the initiator. The vehicle's speed is calculated by measuring the difference between the frequency that reached the vehicle and the frequency that returned.

The radar frequency, or beam, is conical in shape and reaches outward until it is reflected, refracted or absorbed. The range of the beam can be controlled by the operator. Radar disperses its beam and clocks any vehicle that enters that beam.

A benefit of radar is that it can be used in a moving vehicle, whereas a lidar operator must be stationary.

Much like the technology used by surveyors, lidar -- short for light detection and ranging -- shoots a laser at a target to measure its distance and speed. This laser beam is about 1 foot to 3 feet in diameter, and with its approximate 1,000-feet reach, lidar has a wider range than radar. Another advantage of lidar over radar is that it lets police target a specific vehicle.


Closing in on Tailgaters
Lidar's ability to measure the distance between moving vehicles is a relatively new feature of the technology that police increasingly use to bust tailgaters.

The officer sets the gun to measure the distance between himself and the center of a traffic lane. When two cars pass by, the gun tracks the speed of both cars and calculates the distance between them.

The Colorado State Patrol uses this function in heavy traffic to target aggressive drivers as well as speedsters.

"Lidar works extremely well in heavy traffic conditions," said Sgt. Kevin Ratzell. "The laser beam allows the officer to individually pick out a violator's vehicle even while in a group of cars."

The Colorado State Patrol also uses lidar to take accurate measurements at accident scenes by measuring skid marks, reference points and so forth. "This is great stuff that radar does not have the capability of doing," Ratzell said.

The Arizona Department of Public Safety recently purchased nine lidar units and uses them primarily to bust speeding motorists. But a side benefit, and one that the department sought when it made the purchase, was the feature that measures the distance between cars.

"That was one of the benefits we were looking for," said Tom Mason, public information officer for the Department of Public Safety. "Lidars are like a blender; they come with different functions within them. You can get upgraded versions. We elected to purchase them with that extra [tailgating] feature on it. People don't think [tailgating] is dangerous. They don't understand why it's illegal, and we've definitely gotten the message out by using those instruments. It's been a really good tool."

About two years ago, the Newark, Del., Police Department had grant money to spend and considered either lidar units or radar units.

"The decision was to give lidar a chance," said Master Cpl. Curtis Davis. "It wasn't a new technology, but it was technology that was just hitting the mainstream at that time."


Pros and Cons
Newark bought two units then later added five more. Lidar has its place in Newark, but will not replace radar, Davis said.

"In rural environments, open roadways and limited-access roadways, lidar is absolutely fabulous. The range is incredible, and you can zero in on a specific car so that you're not getting the slower vehicle."

The advantage, Davis said, is that if a group of cars is approaching and one is clearly going faster than the others, the officer can target that car.

With radar, any of the cars that come into the stream can trigger a response.

"Laser is different from radar because you're used to throwing it out there, and whoever is going too fast gets stopped," Davis said. "At least with laser you can get the most flagrant offenders."

But Newark, primarily an urban area, has found that there are also disadvantages to lidar.

"In an urban setting it's absolutely horrible, because if a telephone pole gets into the way of your laser -- between you and the car -- or a branch or a sign or anything that interrupts the stream, you have nothing," Davis said. "Radar will go around that sort of thing."

Capt. Lisa Solomon of the Paso Robles, Calif., Police Department said her department found both radar and lidar to be valuable.

"We use lidar on a daily basis. The primary benefit is the small bandwidth of the beam as opposed to radar," she said. "This makes it the best choice for speed-enforcement tools on congested roadways. Our motor officers use it most frequently where traffic is heavy. Lidar is a handheld device that has no moving mode. For patrol officers who have other beat responsibilities, radar usually works better because it is always on and ready as they are driving around.

"If the officer spots a possible violation, he can consult the dash-mounted radar and get instant results regarding speed of a vehicle coming toward him while moving," Solomon continued. "This is really the key difference and the reason a municipal law enforcement agency would want both."


You've Come a Long Way
Lidar has come a long way since the Colorado State Police first toyed with it in the early 1990s. The units then were clumsy and costly, even more expensive than the $4,000 cost of today's unit -- radar units sell for about half the price.

New lidar units are much smaller and easier to handle, and have been likened to a pair of binoculars. Lidar providers are also beginning to produce more options, including digital photo evidence. When the lidar captures a speed violation, it also records a digital picture for evidence. The image shows the vehicle, its speed, the lidar target and a time stamp.

Even with the new options, experts say lidar won't replace radar, but it will be a handy companion that fills a niche, as it does for Ratzell and the Colorado State Patrol.

"We feel lidar will help our efforts to control speed, following too closely, and with the safety of officers at an accident scene," he said.
Jim McKay, Justice and Public Safety Editor Justice and Public Safety Editor