Just after I strap my seatbelt and turn the ignition I remember back to the cover of my Driver’s Ed. book. It had a “55 Alive” logo prominently in the center of the page reminding new drivers of the state speed limit at that time. Because of that logo, I always try to maintain the posted speed limit.
At present I’m currently driving 500 miles per week. Greenfield to Gardner is approximately fifty miles; because the ride gets pretty boring I started paying attention to all the police hideouts. One spot I hadn’t seen an officer hangout was at the crest of the hill, just after exit 19 on Route 2.
About a mile after I passed him I noticed he pulled up behind me and turned on his blue lights. He asked if I had any notion why I was being pulled over and in the pit of my stomach I knew my foot may have slipped on the accelerator. I didn’t hesitate to tell him I knew and went on to explain why I was driving at an unsafe speed.
Since receiving the warning I wanted to better understand how police speed detectors operate. After all, I knew there are two types of guns, but had absolutely no idea how either worked. Radar and laser are the two basic systems in use today. Radar guns can be fixed into a police car or handheld; however, laser is only handheld.
I’m going to start with the older technology first. Police have been using radar since the 1950’s for speed enforcement. Radar emits a set frequency and relies on something called the Doppler effect to calculate the speed of a vehicle.
LIDAR (or LIght Detection and Ranging) is the newer technology and the one that snagged me. These guns are equipped with a laser which bounces a beam of light off a target on the questioned vehicle. Because lasers emit light at a very specific frequency, speed calculations are made differently than radar.
We’ve all experienced the Doppler effect at one time or another. If you stand by a train track or highway you would notice the tone of the oncoming cars or train is higher than when it passes. Sound waves are being compressed by the fast moving cars causing the perceived tone to be much higher.
Police radar sends a broad stream of set-frequency radar from its gun and receives back a compressed wave length frequency from oncoming cars. A computer in the radar gun then calculates the speed the vehicle was passing and outputs it to a display.
LIDAR, on the other hand, sends a beam of light at a specific frequency and times how long the beam takes to return to the gun. Most modern guns used by police average around 200 pulses per second. The computer in the LIDAR gun determines how fast the beam is returned then calculates speed based on a sophisticated algorithm
Coincidentally, around the time I was pulled over I had a chance to use a LIDAR gun. As I experienced, police are able to target a specific vehicle because the LIDAR unit is equipped with a crosshair much like a gun sight. Radar, however, cannot easily target a specific vehicle because it broadcasts a wide path and may sense multiple moving objects.
I was told LIDAR is rapidly replacing radar as the speed detection of choice because costs are declining due to demand. As you travel the highways of America try not to think of ways of not getting caught speeding, but think of all the technology police have in their hands. If you ever see or have seen me travel above the posted speed limit send me a text and let me know. But please don’t send it while you’re driving.
(Jeromy Patriquin is the President of Laptop & Computer Repair, Inc. located at 509 Main St. in Gardner. You can text him directly at (978) 413-2840 or visit www.LocalComputerWiz.com.)