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Radar Unit Accuracy

These days most radar units are extremely accurate. There are some conditions that must be met however, and the conditions are as follows:

  • The road must be flat and straight

  • There has to be good visibility

  • There needs to be a minimum of traffic

  • 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. There are a lot of errors that can occur in routine traffic radar operations.

HOW THE SYSTEM FAILS

The national Bureau of Standards tested the six radar 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 inside or outside 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. Despite the errors found, none of these units were dropped from use. Some of these units are almost certainly still in operation throughout 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 unit 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 distort 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 distort 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 is impossible to avoid if you are using the unit in the “instant on” mode. Errors occur 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 units when the police car is accelerating and the target vehicle is moving at a slow speed, typically under 20 mph and 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 in fact 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 unit finds a larger vehicle between the patrol car and the targeted vehicle and consequently 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 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 occurs which will distort 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 results in a misrepresented reading generated by the vehicle.

In addition to those errors listed above, there are several ways that police officers can actually deceive the reading. This originated because some smaller communities 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 numerous speeding tickets to others

  • 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 a low flying airplane

Set the car mounted unit to calibrate and the unit will register whatever the patrol car vehicle’s speed is at the time

 
 

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