Speed Cameras on the M25

Skeeter

Skeeter

Skeeter

Caporegime
Joined
8 Mar 2007
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Location
Surrey
Are there many? Most gantries have signs and road markings, but very few seem to have cameras (I'm assuming the large grey boxes on the rear side are the speed cameras).

Also, do they change their trigger speeds with the variable speed limits?
 
There's quite a few from junction 9 towards heathrow onwards, yes allegedly they adjust but previously they haven't been working as they weren't "approved" or similar. As you say big grey box. You can usually tell if they are on the upcoming overhead gantry by looking on the other side of the road as they normally did both sides of the road at the same point.
 
Gantry boxes are only on when there's a variable speed limit in effect, in which case you shouldn't be speeding. When they're in effect, 10%+1mph is the rule of thumb, but again, behave yourself as there is likely to be a queue ahead.

Sauce: M25 is the hub of all my travel (1-4k miles p/m) and I'll regularly carry well over a ton through the cameras when it's clear.
 
Supposedly they are able to be moved between gantries which is why they are not on every single one plus are only active when the variable limits are on. However it was in the papers a few weeks ago that no one has been prosecuted for over a year due to the font not being correct on the speed limit signs. Doh!
 
If you see them on the opposite carriageway they are on yours.

I'd be quite happy to be worried about getting caught as most of the time you'll be doing 70 then 10 then 70 then 10 etc
 
Theophany said:
Gantry boxes are only on when there's a variable speed limit in effect, in which case you shouldn't be speeding. When they're in effect, 10%+1mph is the rule of thumb, but again, behave yourself as there is likely to be a queue ahead.

Sauce: M25 is the hub of all my travel (1-4k miles p/m) and I'll regularly carry well over a ton through the cameras when it's clear.
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My wife works for the company that installed & designed the gantry cameras and I can confirm that this is correct. The cameras are only active when there is a speed limit on the overheard signs (this applies when displaying the NSL sign on those boards too).

Top tip - of those grey boxes above the lanes, only one of them actually has a camera in it at any one time.
 
So if they only apply when the signs are lit, they must vary their settings dynamicly?

The variable speeds limits are doing my nut already. They are either 60 when I'm stationary, or 40 when I could easily be doing 70 without any issue.
 
Skeeter said:
So if they only apply when the signs are lit, they must vary their settings dynamicly?

The variable speeds limits are doing my nut already. They are either 60 when I'm stationary, or 40 when I could easily be doing 70 without any issue.
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Surely the reason for them being 40 when it's clear is because there is something further up ahead and they're trying to stop you from speeding up there and joining it? Making it worse?

Just my logic behind it, quite happily be proved wrong though.
 
Skeeter said:
So if they only apply when the signs are lit, they must vary their settings dynamicly?

The variable speeds limits are doing my nut already. They are either 60 when I'm stationary, or 40 when I could easily be doing 70 without any issue.
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thats the whole point of those cameras. To try and keep the flow going. So slowing you all down to 40mph avoids you slamming into the traffic jam further up the road. :)
 
EliotG said:
Surely the reason for them being 40 when it's clear is because there is something further up ahead and they're trying to stop you from speeding up there and joining it? Making it worse?

Just my logic behind it, quite happily be proved wrong though.
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You're pretty much bang on pal.

Blast through when it says '40' and be prepared to, quite literally, stand on your brake pedal. Doing it once is scary enough to make you learn.
 
EliotG said:
Surely the reason for them being 40 when it's clear is because there is something further up ahead and they're trying to stop you from speeding up there and joining it? Making it worse?

Just my logic behind it, quite happily be proved wrong though.
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No, they must not reset them sometimes (or they fail to reset). I've been at night, no one around and it gone 70-40-70 for no reason. (No cancellation sign for the 40 too)
 
Juntions 12 to 9 (maybe further) were 60 last night for absolutely no reason.

In the most part yes, they have a purpose, but not always. And suddenly dropping a 40 causes more issues than it solves as everyone suddenly slows.
 
Looking at the gantry on the other side isn't foolproof. On the way back from London I had time to study this as I was a passenger and whilst 90% of the time the rule works, its not infallible.
 
ci_newman said:
My wife works for the company that installed & designed the gantry cameras and I can confirm that this is correct. The cameras are only active when there is a speed limit on the overheard signs (this applies when displaying the NSL sign on those boards too).

Top tip - of those grey boxes above the lanes, only one of them actually has a camera in it at any one time.
Click to expand...

Useful to know, thanks.
 
ci_newman said:
My wife works for the company that installed & designed the gantry cameras and I can confirm that this is correct. The cameras are only active when there is a speed limit on the overheard signs (this applies when displaying the NSL sign on those boards too).
Click to expand...

I can validate this as I have worked with numerous companies who make this kit (VMS, Techspan, etc.) and the engineers there have all told me the same thing.

The cameras are only active if a speed limit (either the speed in a red circle or the NSL sign) is lit. They also have built in feedback loops that provide court-admissible evidence to prove the sign was working.
 
I did wonder how any photos from the camera would know what was being displayed as the speed limit on the screen behind it.

I'm assuming they are only active when showing a speed limit inside a red circle, and not when its a number with the 4 flashing yellow lights?
 
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