Speed Camera Technology
Speed limit enforcement methods
Speed limits were originally enforced by manually timing or "clocking" vehicles travelling through "speed traps" defined between two fixed landmarks along a roadway that were a known distance apart; the vehicle's average speed was then determined by dividing the distance travelled by the time taken to travel it. Setting up a speed trap that could provide legally satisfactory evidence was usually time consuming and error prone, as it relied on its human operators.
While digital cameras can be used as the primary means of speed detection when combined with automatic number plate recognition (ANPR) average-speed camera systems, their use is more commonly restricted to evidence gathering where speeding offences are detected by various other types of sensors such as such as Doppler radar, piezo strips, infrared or laser devices.
Avoidance and evasion
Some drivers use passive radar detectors or LIDAR detectors to detect police radar or LIDAR signals, with the intention of avoiding or evading prosecution by slowing down before entering an enforcement zone.
In the U.S. state of Ohio, the issue of whether a city has jurisdiction under the Ohio Constitution to issue citations based on speed cameras will be heard by the Ohio Supreme Court on September 18, 2007, in the case of Kelly Mendenhall et al. v. The City of Akron et al.