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Radar And Laser Detectors

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On: Thu, Sep 1, 2011 at 12:42PM | By: Peter C Sessler

Radar And Laser Detectors

For the past 40 years or so there has been an escalating electronics war between the police on one side and motorists on the other who prefer to travel at speeds that are higher than those posted. The reason police use radar and other methods to detect speeding vehicles is primarily a safety issue—the faster you go, the more likelihood there is of having an accident. That may or may not be true, but like everything else, there’s more to it than meets the eye. Besides the safety issue, issuing speeding tickets has become a lucrative source of income for certain localities across the country. You’ll find that small community police forces will prey on unsuspecting out-of-town traffic (mostly) by posting speed limits that are unrealistically low.

Anyway, my personal feeling is that speed limits, especially on the interstates, are routinely ignored by the vast majority of drivers. All you have to do is drive on some of the local Interstates. People drive at whatever speed they feel comfortable—legal or not.

The most common method for police to detect vehicles over the speed limit is the use of a radar gun. Radar guns send out either a pulse or a continuous signal of radio waves and determine a vehicle's speed based on the reflected signal. Police radar uses three bands—X, K, and Ka bands. The X band was used back in the 1970s when K radar was introduced. In the late 1980s, the Ka band was introduced. Today, you’ll find that about half of all police radar guns use the K band, and the rest are pretty much equally divided between X and Ka bands. Practically every radar detector today is designed to detect these three frequencies.

In recent years, police have started to use laser guns or LIDAR. LIDAR is more difficult to detect; however, it has a much shorter range than radar—about 500 feet. So if the police get a good reading on your car, detecting a LIDAR beam before it’s too late is difficult at best. On the other hand, since the laser must reflect directly back to the laser gun off a flat surface, police have to be positioned right in front of your vehicle to get a good reading. Unless the laser is aimed specifically at your license plate or headlights, the signal can bounce off your car in a direction away from the police. In the latter case, a laser detector can be very useful.

Police also use VASCAR. VASCAR is a system that times your car as soon as it passes a specific landmark and stops further down the road. Typically, there will one or two chase cars to apprehend speeders. However, because there will be a lot more radio traffic on police frequencies in such cases, there are scanners that can detect these too.

Photo radar is another system in use. The system measures the speed of a car and if it’s over the speed limit, it will take a picture of the passing car’s license plate as it goes by. A few weeks later, the offender gets a ticket in the mail. There are constitutional questions regarding this system, and, as for countermeasures, there are sprays that can be used on the license plate and license plate covers that can over-expose the film or blacken the plate to the camera. Others recommend angling the license plate downwards a bit.

Because radar detector emit a weak radio signal, police can detect these signals by a device called VG-2. As you’d expect, some radar detector manufacturers have special models that emit no radio signals while others are designed to turn off if they detect VG-2 in the area.

With the exception of Virginia and Washington DC, radar detectors are legal. I haven’t used one in years and, yet, if you drive with common sense, you really don’t need one.


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