Beam-Reflection Error

A police traffic radar’s beam acts like a flashlight or searchlight. It sends out microwaves, which spread out from the source and are easily reflected. Metal objects like cars, signs, and bridges make excellent radar reflectors, reflecting microwaves around at odd angles. However, microwaves are not invisible to a radio frequency receiver, and radar simply transmits and receives these frequencies.

Like a flashlight, there’s a limit to how much area the radar can “illuminate.” Naturally, the greater the power of the flashlight, the more light it puts out. The same holds true for police traffic radars. The effectiveness of the radar depends on two things: the power or strength of the transmitted signal and the reflectivity of the target. Because of tight municipal budgets, police traffic radars generally have low power or strength. For vehicles, radar reflectivity depends mostly on their size and shape. The larger an object, the easier it is for radar to hit it and bounce off of it. The smaller and more irregular the surface area of an object, the lower its “visibility” to the radar signals.

The Texas Department of Public Safety produced a comprehensive manual based on federal tests. It cautions operators, “The radar operator must be familiar with situations that can produce ‘error’ readings.” If the operator does not detect the error, a ticket will be wrongfully issued. One of the radar “errors” detailed by the Texas manual was the “beam-reflection error”:

“Because microwaves are so readily reflected, caution must be taken even in mounting the antenna within a patrol car. They say it’s possible that a reflective path can be set up through the rearview mirror that will produce radar readings on vehicles behind the patrol car when the radar is aimed forward. And those vehicles behind can be either coming or going, since radar does not distinguish directions.”

A traffic radar can be pointed at a freeway with traffic zooming in both directions, but it will only produce a display showing a single number. The traffic radar itself does not pick out which particular vehicle is moving fastest. This is the officer’s job, and that decision is subject to human error. Thus, beam-reflection error describes a situation where the radar is picking up vehicles that are behind the patrol car, when it should be picking up vehicles that are going forward – in a direction in which the officer can give chase.

Traffic radars are still not subject to any government standards. Contact an experienced, knowledgeable New Jersey traffic ticket attorney like Dan Matrafajlo to find out if you have any defenses based on a radar error.


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