Speed controls on roads have been carried out by spot speed measurements (like the police radar) for many years, but due to some of the disadvantages, Average Speed Limit Infringement Detection systems are becoming widely accepted in many places. By means of a series of automatic number plate recognition (ANPR) cameras, usually mounted on a square arch above the roadway, a corridor, rather than a point, can be surveilled. However, whereas the maintenance and calibration of a radar device is sufficient for spot speed measurements, for average speed limit applications the whole system needs to be verified. Without such verification documents, authorities may face legal cases by drivers who object to the speeding penalties issued against. An academic methodology needs to be promptly introduced to the literature for this verification procedure to be undertaken by independent and expert traffic engineers in countries where such audits have become compulsory by law. This technical note will therefore fill in this gap as a guidance document.