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How California Police Determine Speeding

How do the police know how fast you are going, anyway? California police officers have several different types of technology at their disposal to enable them to catch speeders. Radar is the most common. Radar devices can be either mounted in a police car or portable "radar guns." The police do not have to aim the radar at a specific vehicle to get a reading-the radar will pick up all the vehicles on a given stretch of road. Basically, radar devices send out an electromagnetic signal that bounces off of your car. The signal bounces back to the radar device after it hits your vehicle-but due to the Doppler Effect, it comes back at a different frequency. The return frequency depends on how fast your vehicle was going, enabling the police to calculate your speed.

You can buy radar detectors that pick up radar signals and let you know when it's time to slow down, although there's always a risk that the device won't warn you in time. However, laser devices known as LIDAR help police measure your speed without setting off your radar detector. LIDAR devices work by aiming a beam of laser light at your vehicle and measuring the amount of time it takes for the laser beam to be reflected back. They are not available as portable "guns", and they have to be aimed at a specific car to get a reading. However, they are accurate and undetectable to traditional radar detectors. LIDAR detectors are available, but by the time the laser sets them off, the cop already has you in his sights and it’s too late to avoid  a California speeding citation.

Aircraft is sometimes used to spot speeders in California. In most states, aircraft catch speeders by measuring the amount of time it takes a vehicle to travel a known distance. However, this method of measuring speed, known as VASCAR, is illegal in California. In California, aircraft can be used to spot speeders, but officers on the ground must use radar or LIDAR to get a reading of your speed before they can stop you.

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