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 California, the offense of speeding occurs when a driver exceeds the posted speed limit or drives at a speed that is not reasonable and prudent given the current conditions, such as road characteristics, weather, and visibility. California's Vehicle Code outlines the state's speeding laws, which include absolute limits (a specific speed limit) and the basic speeding law (driving at a safe speed for conditions). Penalties for speeding typically involve fines and the addition of demerit points to the driver's record, which can affect insurance rates and driving privileges. Repeat offenses may lead to increased penalties. Law enforcement officers in California use radar and LIDAR technology to measure vehicle speeds. These devices must be properly calibrated and the officers trained in their use to ensure accurate speed detection and to uphold the validity of speeding tickets in court.