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How Illinois Police Determine Speeding

There are several different methods that Illinois police can use to determine speeding. The most common method of measuring speed is by radar, of course. How does radar work? Without getting too technical, here is a simple explanation: radar guns fire off an electromagnetic signal that bounces off your car. The signal bounces off of your car and is reflected back to the radar device. As it bounces off of your car, the frequency of the signal changes, based on how fast your car is traveling. This is known as the Doppler Effect. By measuring the frequency of the return signal, the device can calculate your speed.

Laser, also known as lidar, is another way that police officers can measure speed. Lidar devices shoot a laser beam at your car. Don't worry-it's just a laser, not a death ray! Laser devices measure the amount of time it takes for the laser beam to hit your car and be reflected back, and use this information to calculate your speed. Laser makes it easy for police officers to hone in on one vehicle and get a reading, even in heavy traffic. Since laser is not detected by most radar detectors, it also increases the chances of catching unrepentant speeders who believe a radar detector will keep them safe.

Illinois also uses speed cameras mounted on police vans to catch people speeding in work zones when construction workers are present. This may sound sneaky, but to be fair, a sign on top of the van tells you your speed and is visible from about a 1/4 mile away. The camera doesn't actually catch you speeding unless you are still speeding when you pass the van and the officers inside it. The cameras take a total of 4 pictures: A picture of the driver, a picture of the front license plate, and two snapshots of the back of the vehicle.  Right now, speed cameras are just for work zones, but there is talk in the legislature of using them along the highways to catch drivers going faster than 80 mph.

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