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Radar Wins Speed Test Against GPS

January 02, 2008  | 

A Sonoma County, Calif., judge has ruled a speeding case supported by an officer's radar cannot be thrown out. The speeder's GPS system allegedly recorded a speed contradictory to the radar reading, but the judge ruled radar more reliable.

Roger Rude, a retired Sonoma County sheriff's lieutenant, brought the case to fight a ticket his stepson Shaun Malone received for going 62 mph in a 45 mph zone. Rude had installed a GPS system in the car to track his stepson's speeds. Rude alleged Malone never was speeding based on the GPS tracker.

The court ruled against the GPS data, holding that radar data is more reliable.

JB Harper, Radar Systems Engineer for Decatur Electronics, the manufacturer of the radar that clocked Malone, said radar is a time-tested speed assessment tool.

"Decatur radar has been catching speeders for more than 50 years," he said. "Radar reads a speed at the speed of light rather than calculating geographic and time differences between two separate readings as is done in a GPS system."

Officials with the Petaluma Police Department, which issued the ticket, agreed. Petaluma Police Capt. Dave Sears said GPS is a valuable tool but is not as accurate for tracking speed as radar.

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Comments (4)

Displaying 1 - 4 of 4

kosa007 @ 1/4/2008 2:20 PM

The manufacturer of the GPS should have a say on this case as their product's accuracy and reliability was questioned.

jacob4900 @ 1/6/2008 4:42 PM

I am disappointed to see the results in this article. While there are obviously other issues such as chain of custody, certification, and technical accuracy of the GPS device, I dont think anyone was actually questioning the accuracy of the radar unit itself. Radar officers know that there is an amount of skill and practice required to accurately track and measure the speed of cars in varying conditions. While not making judgements or assumptions without knowing the details of the case, I will say that data from a GPS device that is specifically designed to track the speed of a vehicle makes for a very persuasive argument and I would be extremely interested in the cicumstances surrounding the radar hit in light of a discrepancy. At the very least, it sounds like there should be enough for reasonable doubt here and at face value I likely would have ruled differently.

dcreed @ 1/7/2008 9:41 AM

Assuming the radar and operator were certified I agree with the court's findings. In a properly conducted tracking history the officer assesses the target vehicle speed based off first, observation, secondly the doppler tone, then uses the readout to verify/confirm their tracking history. So the radar is not the only tool in question by the GPS proponents - the offcier's on site real time observation and tracking history are - which outweighs uncalibrated uncertified commercial GPS in my mind.

cajinjedi @ 1/9/2008 9:31 PM

..."a GPS device that is specifically designed to track the speed of a vehicle" uses "averages" and basic math/physics to measure speed. It does not track the acceleration or actual speed of the vehicle; it is simply using a fixed formula to give an average speed. It identifies a location at a time and then at a later time identifies the "new" location. The distance traveled and time elapsed are then used to calculate "speed" (remember speed=distance divided by time). Using this logic, let's say a vehicle is stopped when a location is registered, but accelerates rapidly and travels 1/4 of a mile then stops again (e.g. a dragster). The distance covered is only 1/4 mile and the time between location updates is 20 seconds. According to the math, the vehicle was only traveling approximately 44.99 miles per hour. Using this dragster/drag strip example, the vehicle's speed when in motion is checked by a person actually at the location using radar & the radar registers a speed in excess of 100 miles per hour. Do you see where the radar is considered more accurate? So, if the vehicle is traveling over the speed limit and then rapidly decreases to a speed below the limit (when they see the patrol car), the speed registered by the GPS unit will reflect a speed between the two actual speeds. The radar unit on the other hand will measure and display the actual speed(s) of the vehicle based on more advanced scientific and mathematical equations (the term "Doppler Radar Theory" should sound familiar).

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