The infraction or offense of speeding is committed when the driver of a motor vehicle exceeds the posted speed limit or exceeds the speed limit that is reasonable and prudent under the circumstances or conditions—such as the road (straight, curved, wet, dry, icy, flat, hilly); the weather (clear, foggy, raining, snowing); and the visibility (smoke from a grass fire or a tractor trailer obstructing the view).

Speeding laws (and enforcement) vary from state to state and among cities and towns (local ordinances) and are usually located in a state’s statutes. The penalty for speeding is usually a fine and demerit points added to the driver’s license or driving record.

To measure the speed of a moving vehicle and issue speeding tickets, police officers generally use radar guns that rely on radio signals and the Doppler Effect, or Light Detection and Ranging (LIDAR) technology that relies on lasers rather than radio waves. These devices require training on their proper use and regular calibration to be accurate.

In Illinois, the offense of speeding occurs when a driver operates a vehicle at a speed exceeding the posted limit or drives at a speed that is not reasonable and prudent given the current conditions, such as road characteristics, weather, and visibility. Illinois speeding laws are codified in the Illinois Vehicle Code, and the penalties for speeding can include fines, court costs, and the addition of demerit points to the driver's record, which can affect insurance rates and driving privileges. The severity of the penalty often depends on how much the driver exceeded the speed limit and whether it is a repeat offense. Law enforcement officers in Illinois use radar and LIDAR technology to measure vehicle speeds. These devices are subject to strict regulations regarding their operation, including the requirement for officers to receive proper training and for the devices to undergo regular calibration to ensure accuracy. Failure to adhere to these regulations can affect the admissibility of speed readings in court.