DUI Attorney Blog - Traffic Infractions 

Causes of Inaccurate Radar Reading


Did you know that more than a quarter of traffic violations that are given are done in error? Faulty radar guns, laser guns, and other faulty techniques can cause you to receive a ticket that you should have not received. What makes matters worse; most people who receive traffic tickets pay their fine and never think twice about it.


One of the most common forms of a faulty reading for radar guns and laser guns is interference. Radar guns use the electromagnetic spectrum to help them gauge the speed of a vehicle. Problems arise with interference when the electromagnetic spectrum has multiple forms of energy happening at once. Air conditioners in police cars and power lines overhead are common forms of interference.

Cosine Error

A correct reading on police equipment comes with experience. A cosine error on radar guns, typically happen with inexperience. These faulty readings usually occur due to the angle in which the police care is sitting or moving.


If a police officer is attempting to determine the speed while moving, a shadowing effect is common. This occurs when the officer passes behind a moving object, like a tractor-trailer. Radar guns will pick up the moving truck as the background instead of the real background, causing a faulty reading.

Two Other Common Techniques Used by Police to Detect Speeders are Pacing and Aircraft:


Pacing is commonly used by police to issue speeding tickets. When officers drive behind a car, they can determine the speed without a radar gun or laser. Officers simply follow cars and note their speed using the speedometer in the police car. For pacing to be accurate, the officer needs to maintain the same distance between their car and your car. This must occur long enough for the officer to achieve an accurate reading.

Problems typically arise with pacing if the officer follows you around curves or up or down hills, or if the pace is interrupted by a stop sign. Pacing is one of the least accurate forms of speed measurement, especially if the officer paces you but maintains a great distance between his and your car.

Air Craft Speed Detection

Air craft speed detection is used by officers to detect the speed a car is traveling based on how fast a car travels from one marker to another marker. There is a pilot who uses a stopwatch to determine this speed. The pilot can then inform an officer on the ground to pull you over.

Do not assume because an officer has used one of these speed measuring technologies, that you cannot successfully fight your speeding ticket. On the contrary, thousands of Washington speeding tickets are dismissed each year due to inaccurate readings and other errors. Radar guns, laser guns and other forms of speed measurement are not foolproof.

If you simply pay your traffic ticket, you are admitting the violation that you may not have committed or that you could have beaten in court.