Travelling back from a stay in the Highlands this weekend, I travelled up and came down the A9 (South from Inverness). The whole A9 seems to be a never-ending stream of average speed cameras. This set me wondering how they work. Is your average speed determined multiple times along the road, taking average speed between one camera and the next, or is it avaraged over your whole journey along the A9, or some combination of both?
Along the A9, there are many useful stretches of dual carriageway, allowing for safe overtaking. I know these stretches have a 70, rather than 60 MPH limit so the cameras must take that into account when calculating average speed of a specific vehicle?
I must say that the A9 journey was uneventful, in that no-one was speeding, traffic flowed at 55-60 very smoothly and nobody tried to intimidate you into going faster. I found myself with cruise control set to 58, with nary another car in sight for mile after mile. Rather a refreshing change from the hurly-burly of the M6 etc. ...

Be true to yourself. That way happiness lies...

Same thing on the M1 right now and it got me wondering too,
I accept that speedos are pessimistic but I always stick to the posted limit of 50 and still people are going past a specially trucks, do they ever get a ticket?, who knows. FL2 SD4 Metropolis Auto Santorini Black / ivory completely stock.

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Stop global winging.

I understand these work between any two adjacent gantries. So those who use a stretch of road frequently know if there is not another gantry before they turn off and can go like a bat out of hell with no sanctions. Everyone can spread it - Anyone can catch it. Stay home - the life you save can be your own!

If it's like the setup on the A77, they can track between any pair of multiple of cameras at will.

How this is applied in any particular period is up to police. Andy
Freelander2 HSE (59 Plate, MY10 spec)

I use the southern most part of the A9 regularly and it is lovely not having tools trying to run into the back of you to get past.

I understand there is frustration on the single lane bits where people can get stuck behind lorries which have a lower limit but otherwise I think it is great. No need to speed, or at least I find no need to so it makes the journey far nicer.

As for the dual carriageway parts, you would assume they calculate based on a 70 limit rather than a 60. FL2 TD4 GS 60 reg Facelift - so many issues
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I believe AndyK159 is correct.

Average speed is calculated by two random cameras.

i.e. Your speed may not be simply calculated between one gantry and the next - it might be between gantry one and six (for example), with gantries two through five not performing any function.

As suggested, the gantries that are used can be changed as the situation demands.

Anecdotal evidence suggests that the newer versions of the software can determine for themselves which gantries to use. i.e. Car 1 might have their average speed measured between gantry 1 and 3, whereas car 2 might be measured between gantry 1 and 6......

Not sure how true that is, but it sounds plausible.

Sounds entirely plausible, with software. Key is keep to the limit!  ...

Be true to yourself. That way happiness lies...

There are 6 cameras on a stretch of road I used to use in Yorkshire with 3 on each side, rumour has it that only 3 are working at any time but no one knows which ones. FL2 SD4 Metropolis Auto Santorini Black / ivory completely stock.

It's true that light travels faster than sound, some people look quite intelligent until you hear them speak.


Stop global winging.

Chuckalicious wrote:

stuck behind lorries which have a lower limit

I use the A9 a fair bit and there is now signs saying that lorries can do 50MPH which helps a lot. The dual carriage way sections on the A9 between Inverness and Perth are not part of the average speed camera range which helps too allow you to clear traffic quick as some of these section are not very long. I was under the impression that the cameras only work between each other rather than 1 calculated journey time over them all. However that was just what we have heard up in bonnie highlands could well be wrong. Regards

Alan