Average Speed Cameras.

Car_54

SpekySquarehead wrote: »

FYI.

My good friend is a taxi driver and he had a passenger who put up the average speed cameras on the M8 in Lanarkshire and he said the they hadn't been calibrated and you could speed through them (which was a rumour in the local area anyway). So doing the nightshift one night he went for it and instead of the 50 he drove at 60. Few weeks later the police come to the door saying he ignored his original speeding letter (which he never got). Anyway, I'll get to the point. It went to course and his lawyer said that the speed cameras were too high and so the high winds may have knocked them off slightly and so cannot be guaranteed to give an accurate result. He was let off.

This may be a unique case though but just bear in mind should anyone get caught.

I think the word you wanted was "imaginary".

Robisere

OP: you should be OK, but if not please let us know if any action is taken, there appear to be others here using this same stretch of road.

To anyone "testing" cameras, and/or listening to a friend of a friend, whether they are average speed or instant cameras - speeding is speeding. Limits are there for a reason.

I regularly travel north from the A16 along a long straight into Grimsby, which has AScameras set at 40. However, the system is sensibly set to go from 60 to 50, then 40 for the stretch where the AS cameras are, until very close to town, when it goes to 30. Every driver travels below the limit in the 40 zone, because there are also traffic lights at intervals, which have complex junctions. Interestingly, the 40 zone used to be 30, but hunderds of complaints about congestion caused the change. And yet the traffic does not really travel much faster than 30 now, due to the effect of the aforementioned traffic lights.

glennevis

GeorgeMcFarlane wrote: »

Would u say the sat nav is more accurate than tha car speedo. As I say I'm a newish driver and can't get my head round it all.

OP a car speedo has to be designed with a tolerance of up to +10% and -0%. That means it is allowed to over report actual speed by up to 10%. It is not allowed to under report speed at all. So when your speedo says 60 and your GPS says 55 the GPS is likely to be spot on.

On the M74 the sat nav would have a clear sight of the satellites (no tree cover or tunnels for example) so is very accurate. It does take a few seconds to catch up if you change speed suddenly but on a motorway that doesn't often happen.

Hoof_Hearted

I am sure that average speed cameras have a bigger tolerance than fixed cameras as roads tend not to be straight. There is going to be some difference in distance doing 50 around the inside of a curve and the outside. I don't think you will have any trouble at all, given the circumstances you outline.

Mercdriver

On a side note, I wish people would learn to drive on ASC roads properly. Over the last few years, ASC's have been put in between junction 42 and 40 of the M4. It causes a bottleneck as people slow down to 30, either to be doubly sure or in the misguided view that if you drive at 70 between them and brake just before the lights that you won't get caught. I suspect it's a mixture probably around 70 - 30 in favour of people being over cautious.

Car_54

Hoof_Hearted wrote: »

I am sure that average speed cameras have a bigger tolerance than fixed cameras as roads tend not to be straight. There is going to be some difference in distance doing 50 around the inside of a curve and the outside. I don't think you will have any trouble at all, given the circumstances you outline.

Roads may not be straight, but generally the LH bends will cancel out the RH bends.

The obvious extreme exception is the M25. But if that were a perfect circle, and lane 1 was 188 km around, then lane 2 would be 188 km plus 23 metres, i.e. a negligible difference of about 0.01%.

wongataa

Hoof_Hearted wrote: »

I am sure that average speed cameras have a bigger tolerance than fixed cameras as roads tend not to be straight. There is going to be some difference in distance doing 50 around the inside of a curve and the outside. I don't think you will have any trouble at all, given the circumstances you outline.

Why would curves have an effect? The system needs to know the distance between each set of cameras on each side of the road. You just measure each distance whatever the path of the road. Each gap doesn't have to be exactly the same so bends are accounted for.

neilmcl

wongataa wrote: »

Why would curves have an effect? The system needs to know the distance between each set of cameras on each side of the road. You just measure each distance whatever the path of the road. Each gap doesn't have to be exactly the same so bends are accounted for.

Because on multiple lane roads the distance may be different for each lane (for example on a road with mainly left hand bends the distance is less on the inside lane than the outside and vice versa) so the cameras must have a tolerance to take this into account and the fact that you could be changing lanes between cameras.

Aylesbury_Duck

As Car 54 has correctly stated, the distance differences involved are negligible. If you take a circular motorway route where the circle traced by the centre of lane 2 has a 50km diameter, and assume that the centre point of lane 1 going clockwise is 5m further out than lane 2 inside it, the difference in the circumferences of lanes one and two over a complete circuit of the motorway is pi times the difference in diameter (10m over the entire circle of motorway). In this case, lane one is 10m x pi longer than lane 2. About 31.4m, but that's over a distance of 157,079m. That's 0.02%

There's no need for any tolerance for curves when the distances between lanes are negligible compared to the radii of the curves.

Car_54

Aylesbury_Duck wrote: »

As Car 54 has correctly stated, the distance differences involved are negligible. If you take a circular motorway route where the circle traced by the centre of lane 2 has a 50km diameter, and assume that the centre point of lane 1 going clockwise is 5m further out than lane 2 inside it, the difference in the circumferences of lanes one and two over a complete circuit of the motorway is pi times the difference in diameter (10m over the entire circle of motorway). In this case, lane one is 10m x pi longer than lane 2. About 31.4m, but that's over a distance of 157,079m. That's 0.02%

There's no need for any tolerance for curves when the distances between lanes are negligible compared to the radii of the curves.

Even more negligible (?) in practice, as the distance between lanes is only 3.65 metres.