Are average speed cameras accurate?

I travel through both inner and outer London boroughs and several cameras are in 20mph zones. However the other week I noticed a camera (the older style GATSO yellow one) with no speed markings on the road so have assumed it is decommissioned and another cameral marked as a 20mph speed camera at a set of traffic lights which doesn't go off if you drive through at a faster speed which means it is a traffic light camera and only activates when you go through it on a red light. Have set off two sets of cameras a while ago without receiving any notification.

I think one possible answer is that once the local authorities have the money they will make a massive upgrade to all the existing cameras and replace them with the new generation of digital two-way models. Until that time we are probably safe.

Also in my local area we have sections of dual carriageway monitored by average speed cameras set at 40mph. Do you know if they can set them for lower speeds? I have a feeling that this cannot be done accurately.

Asked on 11 December 2023 by Neil Littman

Answered by David Ross
The situation regarding deactivated speed cameras is unhelpful for drivers with the potential to cause confusion.

The majority of average speed cameras operate on a time and distance calculation, so in theory will be highly accurate. Rather than being adjusted for lower speeds, it is more a matter of the constabulary deciding at what speed they will decide to issue fines.
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