Police Radar Guns

Police radar gun mistakes, errors and inaccuracies exposed.

By Lawrence Black

Today, most radar guns are extremely accurate. There are some conditions that must be met however and these conditions are as follows:

The road must be flat and straight.
There has to be good visibility.
There needs to be minimum traffic.
And the officer has to be properly trained to interpret false signals generated by the equipment.

It's very rare to find these four conditions existing at the same time. As a result, there are many radar gun errors that can occur.

How the system fails

The National Bureau of Standards tested the six radar gun units most often used by police departments. All of them produced signals that were false from police radios or CD units. All of the units produced panning errors, when used either out or in of the police cars.

There were shadowing errors that appeared on all the units when the police cars speed was added to the targeted vehicles speed. 24 models were tested by the International Association of Chief's of Police for five different manufacturers.

Those results were even worse than that conducted by the National Bureau of Standards. In spite of the errors found, none of these radar units were dropped from use.

Some of these units are still probably in operation around the country today. Radar errors can be a combination of many factors but are all linked to one of the following 13 types of errors found.

Panning - This happens when the hand held radar gun is swept across the dashboard of the car or the control unit mounted to the dash of the car.
Mechanical Interference - The a/c or heating fan in the police car, alternator, ignition noises, rotating signs near the roadway, anything mechanical that is operating in the vicinity of the roadway can throw off the readings.
Shadowing - All moving radar units have this problem since the targeted speed is calculated by subtracting the speed of the police car from the closing speed of the target.
Batching - This error is caused when the police car is either slowing down or accelerating when the radar unit is still calculating the speed of the targeted vehicle.
Radio or Microwave Interference - Any outside source of a frequency transmission such as a CB radio, Ham or police radio, radar from a local airport, cell phones, power lines, neon or mercury vapor lights, power sub stations, etc., any one of these interference's can throw off the calculations of the radar unit.
Auto Lock On Wrong Target - The National Highway Traffic Safety Administration suggest that you disable the auto lock on units that have this function and the newer units no longer have this capability.
No Tracking History - This recommendation is most often ignored. It's one that is stressed in the operational manual and its impossible to avoid if you are using the unit in the "instant on" mode. The errors occurs when there are multiple targets in the path of the radar beam and the police officer has not observed the average speed reading nor has he checked for any external interference.
Harmonic Error From Phase Lock Loop - This problem is common with moving radar guns when the police car is accelerating and the target vehicle is moving at a slow speed, typically under 20 mph and an error can occur in the reading.
Terrain Error - One common factor in radar units is that they always read in a straight line. They cannot read around a turn or the other side of a hill. In this case, the radar unit may actually may be reading another vehicle farther up the road rather than the target vehicle that is going to be issued a citation.
Look Past Error - In this case the radar gun finds a larger vehicle between the patrol car and the targeted vehicle and locks on that one and gives an entirely different reading for an entirely different vehicle.
Multiple Bounce Error - These occur usually when there is an overpass in the vicinity of the chase and the radar beam is reflected off of multiple targets at the same time. The vehicle in question, an overpass, a sign, etc. will result in an improper reading.
Reflection Error - If the antenna part of a radar unit is hung on the outside of the police officer's car , the beam can actually hit a side window or part of the window and a false reading results which will throw off the actual reading for the targeted vehicle.
Arm Swing Error - When the officer swings the unit up to point at the targeted vehicle, the speed of his arm is added to the speed of the vehicle and throws off the reading generated by the vehicle.

In addition to these errors listed above, there are several ways police officers can actually cheat on the reading. This has come about because some smaller communities have found that traffic tickets are an extremely effective way to raise money for their budget. These intentional errors may include the following:

Target one vehicle that is speeding and give out many speeding tickets to other people.
Whistle into the CB on the patrol car which will give out a high frequency pitch and will alter the speed that shows up on the radar unit.
Aim the unit at the ground and swing the unit up into the air.
Clock an airplane that's flying very low.
Set the car mounted unit to calibrate and the unit will register whatever the patrol car vehicle's speed is at the time.

Learn how to beat radar speeding tickets.