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Strict Standards: Declaration of Walker_CategoryDropdown::start_el() should be compatible with Walker::start_el($output) in /home2/chic5563/public_html/JD/wp-includes/classes.php on line 678 » Blog Archive » Got a Speeding Ticket? - Why Radar & Laser Speed Guns are Inaccurate.

Got a Speeding Ticket? - Why Radar & Laser Speed Guns are Inaccurate.

Stay Out of Trouble View comments

Police radar and laser speed guns can be extremely inaccurate.  Not only are they subject to user error caused by inexperienced police officers, their accuracy can also be compromised by environmental factors, multiple vehicles or other moving objects in the area, the speed and movement of their patrol car, and the angle that they use to measure vehicles speed.

Pulled Over

Not only is the equipment inaccurate, but the officers themselves are usually bias due to the fact that their department is atleast partially funded by the citations that they write.  The CHP (California Highway Patrol) is almost entirely funded by the fines that their officers issue. 

There are so many ways to cheat the current system, so it’s not surprising that so many tickets are issued by law enforcement agencies across the country.

Environmental Factors

There are many environmental factors that could greatly effect the accuracy of the police radar guns.  Since radar and laser reads the speed of a moving object they can be greatly affected by the movement of the police cruiser.  If they are shooting radar while moving behind a moving car, their reading could be affected by the speed of their cruiser and this can even more true if they are measuring the speed of an oncoming car. It is extemely difficult to calibrate the constantly changing speed of their car to their radar gun, so they most likely won’t have an accurate speed reading if their vehicle is moving as well.  That’s why most officers prefer to hide and shoot radar or laser from a stationary position.

Driving in Rain

Wind, rain, and snow can also greatly effect the speed readings that they can receive and so can all the electrical equipment in their car. 

Radar/Laser Positioning Issues

The radar or laser speed guns work in a line of site manner, neither can bend around curves nor can they follow the contour of the hilly terrain.  If the gun is not properly positioned, it may seem to clock the next approaching car when it’s actually clocking another car in the background.

Positioning ErrorPositioning Error

Look-Past Issues

Even if the officer aims his gun properly, the radar gun is still subject to the look-past error.  This is caused when the radar passes a smaller vehicle in the front and hits a larger vehicle behind the smaller one.  The smaller vehicle only sends back a small amount of the radar waves and the bigger truck sends back a bigger signal.  Thus the speed of the larger vehicle in the back is being measured and not the smaller vehicle in the front.

Look-Past Error

It’s a common mistake among officers to think that their radar reading will always be measuring the closest vehicle and not another vehicle thats further away.  There are times due to geographic and traffic conditions that the closest vehicle is not the one being measured.  Generally larger vehicles give off large signals and can have their speed measured from further away.
Vehicle Interference Issues

This type of error usually occurs when an officer is using his radar or laser gun from a moving police cruiser.  The traffic ahead of the cruiser can confuse the radar or laser gun’s estimated speed of the patrol car.  These moving radar or laser guns calculate the target speed by subtracting the speed of the patrol car from the speed of the cars in front of them.  These type of readings are subject to 5-10 mph inaccuracy, which can cause an erroneous speed reading which can lead to a speeding ticket.  Slower vehicles can also throw off the speed reading if the officer is behind the vehicle in question, that’s why it’s always more accurate for the officer to measure a vehicle’s speed when he is behind them with his own speedometer rather than his laser or radar gun.

 Look-Past Error 

Cosine Issue

A cosine error is caused by a stationary object on the side off the road.  This object could be a building, a broken down car, or even a sign.  This stationary object can reflect radar signals which can interfere with the reading on the radar gun.  If this object reflecting the radar signals was straight ahead on the road, it wouldn’t interfere with the reading much, however if the object is located at the right angle it might interfere with the reading of the moving patrol car’s speed (making it less) and thus the car in front of the patrol car would be measured higher than the actual speed. 


Double Bounce Issue

Radar works when microwave beams are reflected off of objects.  Sometimes the reflection occurs accurately and other times there is a bad reading where they are actually measuring several objects rather than just one vehicle.  This can either make their reading higher or lower than their actual speed.

 Double Bounce Error

Reflection Issue

Police radar guns mounted inside of police cruisers can be reflected off of the rearview mirror making the readings inaccurate.  Street signs can also effect the readings on police radar guns.

Reflection ErrorReflection Error

Issues with Laser Guns

Police radar guns are far more accurate than the traditional radar guns.  However they are only accurate to 1000 feet.  At 1000 feet the laser beam is around 36 inches wide which can accurately applied to a single vehicle.  However, at 2000 feet the beam expands to 72 inches wide and becomes far less accurate.  It’s also more likely that they will be measuring the speed of another car at this distance.  So if you are pulled over by a laser gun, find out the distance and if it’s over 1200 feet than you have a far chance of fighting it due to the inaccuracy at this range.

Police Laser Gun

Generally officers target a front or rear license plate. If you don’t have a front license plate, they will try to target a headlight which is far less accurate and more prone to errors and false reading off of other cars.

Police Laser Gun Angle

Also the angle at which the laser hits the car will effect the reading.  If the car is hit head on it will have a more accurate reading than if it were hit at a 45 degree or 60 degree angle.

Get a Good Radar/Laser Detector

Valentine One

The Valentine One is one of the highest performing radar detectors on the market. One reason for this is multiple radar antennas! The only other detector with two radar antennas is the Bel STi Driver, but in the STi both antennas face forward. In the Valentine One, there is one forward antenna and one rear-facing antenna. Using this combination of antennas, it effectively tells you the band and strength of the radar signal, along with the number of “bogeys,” or radar units being detected. It will also tell you what direction the signal is coming from, and provide the best rear detection out of every other windshield-mounted detector on the market. Even when this sounds too good to be true, theres more. The Valentine One has excellent laser reception, consistently appearing at the top of tests in this category.

Escort Passport 9500i

Escort Radar 9500i Blue

The all-new PASSPORT 9500i, has revolutionized the radar detector category again. Its blistering performance is derived from the “World’s Best” PASSPORT 8500 X50, which means it delivers the best protection possible against all speed measuring devices. We added advanced GPS-powered intelligence, which makes the PASSPORT 9500i the best performing, quietest and most user-friendly radar detector ever designed.

Escort Radar 9500i

There is a GPS based database which keeps track of known speedtrap locations and photo radar cameras and your detector will use GPS technology to track your position and alert you when you approach these known police hot spots.  It can also measure your current speed to do speed variable detection.


The factors above can all be used to dispute speeding tickets in court.  They can be used to prove the inaccuracy of the radar or laser gun according to the situation and environment where the speed reading took place.  If you want to fight a ticket it may be beneficial to hire a traffic attorney. 

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Comment by Ryan
2008-01-23 09:38:42

Cool tips. I will have to remember these if I ever get pulled over. It seems that officers either give out speeding tickets too easily or they give them out for blatent speeding cases.

They should not have quotas! Quotas on tickets only encourage them to give out unfair speeding tickets.

Comment by Brian Williams
2008-06-20 07:57:20

Let Us Drive…SPEEDING:driving TOO FAST for the CONDITIONS!!!!!!!!!!

Comment by Erick
2010-05-06 04:03:13

they are very useful tips. driving on condition of environment.

Comment by bill
2010-05-06 05:46:31

valentine one does work quite well for detecting speed traps.

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