RE: Lorries make scameras inaccurate
Wednesday 2nd November 2005
Rumbles cause inaccuracyHeavy lorries are causing Gatsos to record false readings, according to one report. The phenomenon has been admitted by the Lancashire Partnership for Road Safety, the speed camera operator, which has called it the shutter effect.
Lorries make scameras inaccurate
Bad vibrations result in incorrectly issued speeding tickets
Rumbles cause inaccuracy
It's caused by the vibrations generated by juggernauts as they grind past. Accompanied by continuous heavy lorry traffic, one camera on the A59 near Preston reportedly flashed every car that went past, irrespective of speed.
The problem's not confined to the UK either. In Australia, where so many roads are long and empty, but the speed limits are low, New South Wales authorities have been forced to annul 26 inaccurate tickets dished out by speed cameras in similar circumstances. For instance, a bus with a maximum speed of 82mph was ticketed for a speed of 87mph. Eventually, the particular camera was removed - even though it was generating AUS$1 million annually in fines.
The Lancashire authority said, however, that it had issued no such inaccurate tickets.
Discussion
esselte said:
Yep. Absolutely true. I got flashed on the A556 doing about 43 in a 50 zone! Couldn't figure why, but I just happened to be along side an Artic. lorry at the time!
Didn't get a ticket luckily!
Could it have been flashing the artic for exceeding it's 40mph limit?
how can it defferentiate between a car and a truck?
apache said:
Yep. Absolutely true. I got flashed on the A556 doing about 43 in a 50 zone! Couldn't figure why, but I just happened to be along side an Artic. lorry at the time!
Didn't get a ticket luckily!
Could it have been flashing the artic for exceeding it's 40mph limit?
how can it defferentiate between a car and a truck?
Is there no difference between the radar return from an HGV and a car?
esselte said:There is a difference: the returned radar intensity.
Yep. Absolutely true. I got flashed on the A556 doing about 43 in a 50 zone! Couldn't figure why, but I just happened to be along side an Artic. lorry at the time!
Didn't get a ticket luckily!
Could it have been flashing the artic for exceeding it's 40mph limit?
how can it defferentiate between a car and a truck?
Is there no difference between the radar return from an HGV and a car?
kinetic wouldn't have got a ticket because whoever processes the photos will have confirmed that kinetic was within their applicable speed limit.
[edit]
"The unit {GATSO} can also differentiate between large vehicles and cars by the amount of radar return, so a lower activation threshold can be set for large goods vehicles and coaches. This explains why sometimes you see a truck that is doing 70mph on a dual carriageway trip a camera when a car at the same speed does not - it has registered that the truck was going too fast (trucks are limited in top speed)."
www.speed-trap.co.uk/Accused_Home/Gadgets/Gadgets_Home.htm
>> Edited by smeggy on Wednesday 2nd November 13:44
smeggy said:
Yep. Absolutely true. I got flashed on the A556 doing about 43 in a 50 zone! Couldn't figure why, but I just happened to be along side an Artic. lorry at the time!
Didn't get a ticket luckily!
Could it have been flashing the artic for exceeding it's 40mph limit?
how can it defferentiate between a car and a truck?
Is there no difference between the radar return from an HGV and a car?
kinetic wouldn't have got a ticket because whoever processes the photos will have confirmed that kinetic was within their applicable speed limit.
[edit]
"The unit {GATSO} can also differentiate between large vehicles and cars by the amount of radar return, so a lower activation threshold can be set for large goods vehicles and coaches. This explains why sometimes you see a truck that is doing 70mph on a dual carriageway trip a camera when a car at the same speed does not - it has registered that the truck was going too fast (trucks are limited in top speed)."
www.speed-trap.co.uk/Accused_Home/Gadgets/Gadgets_Home.htm
>> Edited by smeggy on Wednesday 2nd November 13:44
Thought this was the case.
Yes but the intensity is part of the measurement to determine the speed. I wasn't aware they could be adjusted to return on certain vehicle sizes but considering the static siting and known returns it makes sense. Usually these are set to be triggered by cars as far as I was aware and can't do both because you have to 'anticipate' the return intensity to get a useful speed reading. I'm working backwards from military applications where speed wasn't so important as location
Would this not mean all speeding tickets from Gatso's could be avoided... they'd just fall through.. There could be lorries out of shot etc..
This is good news
- The more flaws they find, the closer they will get to removing 'em
But to be honest it's unlikely. I just wish they'd get rid of the
speed bumps..
Dave.
This is good news
- The more flaws they find, the closer they will get to removing 'em But to be honest it's unlikely. I just wish they'd get rid of the
speed bumps.. Dave.
UncleDave said:
Would this not mean all speeding tickets from Gatso's could be avoided... they'd just fall through.. There could be lorries out of shot etc..
This is good news
But to be honest it's unlikely. I just wish they'd get rid of the
Dave.
I think for an offending vehicle to be out of shot on a Gatso it would have to be going at around 200mph? Even with no limiter I don't think an HGV could manage that
MR2Mike said:
Yes but the intensity is part of the measurement to determine the speed.
No, the gatso uses the change in frequency of the returned signal to determine speed. The amplitude would depend only on the distance and size of the target, not speed.
Of course, seems I've gotten my theory back to front after all these years
Using return intensity to determine target size is very inaccurate because the shape of the target affects the return almost as much as its size. For example the corner of a Routemaster at the right angle could look like the back of an Escort van in terms of echoing area.
The phenomenon being observed with the heavy vehicles is, I believe, called common mode interference and it is feasible that the resonant frequency of the post that the Gatso is mounted on is involved. The signal processing is incapable of differentiating between a true Doppler frequency and an amplitude modulated echo caused by physical vibration of the transceiver. As the target in the latter case is the surroundings, it will always be bigger than the echo from a car.
The phenomenon being observed with the heavy vehicles is, I believe, called common mode interference and it is feasible that the resonant frequency of the post that the Gatso is mounted on is involved. The signal processing is incapable of differentiating between a true Doppler frequency and an amplitude modulated echo caused by physical vibration of the transceiver. As the target in the latter case is the surroundings, it will always be bigger than the echo from a car.
Forget the fancy techie talk and theory - ABD say that at least one Gatso is set to do that - From the local issues section of ABD site, under Warwickshire
"A5 Speed Camera Targetting HGVs at 40
The speed camera on the A5 Eastbound just prior to the A444 Junction is able to distinguish between cars and HGVs, and has been setup to catch HGVs exceeding the 40mph single carriageway limit.
The speed camera is well hidden by a large tree and a large speed camera sign — it's the only example we have of a camera being hidden by it's own warning sign!"
"Propaganda from Warkwickshire Talivan suggests other speed cameras in Warwickshire may also have been setup to increase their takings."
www.warwickshire.gov.uk/Web/corporate/pages.nsf/Links/8FB9E28692F20A7C80256E6E0056FC0B
"A5 Speed Camera Targetting HGVs at 40
The speed camera on the A5 Eastbound just prior to the A444 Junction is able to distinguish between cars and HGVs, and has been setup to catch HGVs exceeding the 40mph single carriageway limit.
The speed camera is well hidden by a large tree and a large speed camera sign — it's the only example we have of a camera being hidden by it's own warning sign!"
"Propaganda from Warkwickshire Talivan suggests other speed cameras in Warwickshire may also have been setup to increase their takings."
www.warwickshire.gov.uk/Web/corporate/pages.nsf/Links/8FB9E28692F20A7C80256E6E0056FC0B
esselte said:
I think for an offending vehicle to be out of shot on a Gatso it would have to be going at around 200mph? Even with no limiter I don't think an HGV could manage that
But if you were snapped in a Focus, you could just argue there was a lorry in front of you that wasn't snapped? Inaccurate claim Mister Plod
Dave.
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