Quick answer
Instead of measuring your speed at one exact point, average speed cameras compare the time taken to travel between camera locations and calculate your average speed over that distance.
This means slowing down only when you see a camera is not the same as staying within the limit across the full monitored section.
How average speed cameras work
1. First camera records vehicle
Your number plate is captured at the first camera point.
2. Later camera records again
Your vehicle is identified again further along the route.
3. Travel time is compared
The system compares the time taken over a known distance.
4. Average speed is calculated
If the average is above the limit, enforcement may follow.
Where average speed cameras are commonly used
- ✓Motorway roadworks
- ✓Long dual carriageways
- ✓Urban routes with safety concerns
- ✓Tunnels or controlled corridors
- ✓Routes with repeated speeding problems
Common myths and mistakes
- !Speeding early and slowing later can still leave your average above the limit.
- !Changing lanes does not automatically avoid average speed systems.
- !Only braking near cameras may not help.
- !Temporary speed limits in roadworks still matter.
- !Assuming cameras always flash can be misleading.
Fines and enforcement
Average speed cameras can be used to enforce speed limits in the same way as other camera systems. If your average speed is recorded above the limit, you may receive a notice, fixed penalty, course offer or further action depending on the case.
For a full explanation, read our Speeding Fine UK Explained guide.
How to drive through average speed zones
- ✓Know the limit before entering the camera zone.
- ✓Keep a steady speed rather than braking late.
- ✓Leave safe space from the vehicle ahead.
- ✓Watch for changes in roadworks or temporary signs.
- ✓Do not rely only on sat nav speed warnings.
Helpful UK speed limit guides
Frequently asked questions
Do average speed cameras flash?
Not always. Many systems do not rely on a visible flash, so you should not assume nothing happened just because you did not see one.
Can average speed cameras work at night?
Yes. Many systems are designed to operate day and night.
Are average speed cameras only in roadworks?
No. They are also used on some permanent routes, tunnels and controlled corridors.
Can changing lanes avoid average speed cameras?
No. Changing lanes should not be treated as a way to avoid enforcement.
Do average speed cameras measure every vehicle?
They can monitor vehicles travelling through the camera zone. The safest approach is to stay within the posted limit across the whole section.