Motorway Signs

[lankeela]

I know this should be in motoring, but I am sure someone out there will know - on the M25 at the roadworks near the junction with the A10 tunnel, there are signs that say 'Average Speed Cameras'. Does this mean that the speed cameras are not very good, only average (!) or what does it mean? Do they take an average of what speed the motorists are doing, if so how do you know when you are over the speed limit? The signs say 40 mph.

[heathfield]

They've installed two sets of these in Scotland, though only one set is working, (they haven't yet put the signs up for the other). They're number-plate recognition cameras operating as a pair at a set distance apart, be it a couple of miles, or even 20 miles.. From your number-plate, they work out your average speed over the distance. Beware!!

[lankeela]

Wow, how scary is that! Thanks heathfield, so does that mean you can go just over the limit for a little way, but if you are below it for more distance, the average would work out under the limit? Not that I ever go over the limit, of course!

[Fat Boy]

That's exactly what it means - if you break the speed limit for one bit you'll have to go slower than the limit before you reach the second camera. If you chose to drive like that you would have to work out how far you were travelling at the high speed and then calculate how slow to go for such and such a distance to even it out.

Not only is it just easier to stick to the speed limit, you'd reach the second camera at the same time anyway.

You ask "how do you know when you are over the speed limit?". Errrr, well, the same way you would do on any other stretch of road - by making a mental note of the speed limit written on the road sign. If you're driving faster than that then you are over the speed limit.

[gary baldy]

These are popular in road works.
They clock you on entering and leaving the road works and at several points in between.
From this it works out your average speed through the roadworks and not just the speed when you slam on the hammers when you spot a camera.
Bobs your uncle - fine and points and not a flash in sight!

[Starman 2112]

I heard that these cameras are going to come into operation on the M4 as well.

[Catso]

And I think the long-term plan is to have one every mile or so on every road.

Said not entirely tongue-in-cheek.

[wilsonator]

Look up SPECS cameras on google, it will tell you what they are!

[lankeela]

Thanks folks.