Hi,
When travelling along the M42 or M6 in the Midlands, there are Active Managed zones which all have variable speed limits according to the gantrys above.
My question is, when travelling towards one that is set at 60 mph, if its drops to 50 mph a few cars lengths before the gantry, is that camera active at the new speed immediately or is there a grace period for the new speed?
This happened to me earlier today so wasn’t too sure…
answered appreciated
Thanks
IF YOU SEE A DOUBLE FLASH, you’re nicked son. 
There is a grace period, it varies between 1 minute and 5 minutes depending on the online source.
Highways Agency say 1 minute…
so there is a grace period, also when they are off, are they set at National limits??
gurj254,
Don’t quote me on this, but from EXPERIENCE, when there is no mandatory speed limit displayed on the matrix, it would APPEAR that the cameras are not active.
Many drivers (possibly myself included), seem to travel through these sections at 80-90 MPH for many tens of miles, with no flashes/letters/convictions or whatever.
It appears that the cameras are only active when there is a mandatory speed limit displayed on the matrix, but that the national limit i.e. 70 MPH is NOT enforced*. Again, don’t quote me on this!
edited to say * Unless it is a ‘70’ surrounded by a red circle! I also exercise caution when the ‘national speed limit’ symbol is displayed, for example when leaving an area of reduced speed.
With regard to no enforcement, I’m referring only to when NOTHING is displayed on the matrix
They do snap away when nothing is displayed, the only ones I have heard of were +100mph so that may be the set limit
Ive sat at 90 on the m2 through the cameras and didnt get a ticket but i know of someone getting caught at 79mph on the m6 but cant remember if he said the signs were up.
Saaamon:
Ive sat at 90 on the m2 through the cameras and didnt get a ticket but i know of someone getting caught at 79mph on the m6 but cant remember if he said the signs were up.
Those V8 Scannies do go well
I’ve noticed on the clockwise M25 around the J10-J15 area, there will often be no limits on the gantries themselves, but then some teararse races through doing the ton in a sports car, and sets the double flashes off. In other words, they ARE on and active, even when there’s no “50” or whatever flashing on them. 
It still amuses me to see all the other cars instinctively hit the brakes as the double flash comes, even though teararse was passing them like they were standing still. 