Ok here's what happened...

I was approaching the junction which I've driven up on many times, I'm aware that there is a camera here so I'm always very cautious. On this occasion I saw it turn to orange and looking back I probably should have just proceeded but I slammed on the brakes and stopped and it was still amber at this point. But then I realised I was very close to the stop line, infact I'm very sure my front bumper might have been above the stop line as I stopped so I reversed back a little exactly the moment the light turned red, to simply ensure I was clear of the line.

I've reviewed the dashcam footage and it's very hard to tell as the dashcam view perspective is obviously quite different compared to the view from the driver seat but it appears that my front bumper may have on top of the line if not slightly over it. Really not sure but in any case I obviously did not go through a red light! So that's why I was asking - surely they can only prosecute you if you've actually gone through a red light rather than just a small part of your front bumper slightly over the line on amber and then reversing back my bumper may have behind the line.... Again I'm not sure how the angle of the red light camera could even tell if the car bumper is over the line.

You'll be fine. Don't worry about it.

how does it know if you have stopped before the stop line at a junction?

They don't detect that the vehicle has stopped. They detect whether it has crossed the stop line after the lights have turned to red, They do this by means of sensors buried beneath the surface just beyond the line.

I'm guessing these sensors are the black lines in the shape of the rectangles just behind the stop line and then in front of the stop line, like in this example here - maps.app.goo.gl/4KseUs8mNq5JLG5e8

So in order for you to be caught going through a red light, your front tyres would have to cross BOTH black lined rectangles, thereby proving you have gone through the red light? And the two rectangles would trigger the the double flash? So your tyres go over the first set of rectangle, first flash, then go over the second, second flash?

Edited by johnmazda on 21/04/2024 at 11:44

I read somewhere red light cameras have 2 second delay. This is to ensure if front of the car crosses the line in amber and then light turns red before rear of the car passes line it will still be clear.

Some long lorries got caught by this, but cars should be fine.

It is to punish drivers who deliberately crossed red light rather than accidental amber gamblers.