Tripping a speed cam from a standstill
Discussion
Petrolhead_Rich said:
Vipers said:
Formula 1 perhaps? Just guessing.
According to Top Gear Tests a "Reasonably Priced Car" (Lacetti) is faster than an F1 car off the line! Anyone remember the tests they did (in the Birmingham NEC IIRC)A Gatso failed to trigger at 145mph / 233kph (Top Gear).
If a Gatso triggers, one could assume there are speed marking for verification (this may not be true, the upper limit for verification may be lower than 145mph).
A Gatso camera fires with a 0.5 second interval (?).
A car travelling at 233kph travels around 64m per second, thus travels 32m in the time between flashes. One could then assume that the road markings do not stretch further than 32m beyond the point at which the radar detection starts (which is presumably only a short distance from the Gatso).
This would give the maximum length of road markings to be around 32m plus a couple of metres to allow for the angle of the radar detector.
Also note that you need to be travelling at the illegal speed 0.5 seconds before reaching the end of the road markings so that the two photographs occur within the road markings.
Anyone good at maths?
If a Gatso triggers, one could assume there are speed marking for verification (this may not be true, the upper limit for verification may be lower than 145mph).
A Gatso camera fires with a 0.5 second interval (?).
A car travelling at 233kph travels around 64m per second, thus travels 32m in the time between flashes. One could then assume that the road markings do not stretch further than 32m beyond the point at which the radar detection starts (which is presumably only a short distance from the Gatso).
This would give the maximum length of road markings to be around 32m plus a couple of metres to allow for the angle of the radar detector.
Also note that you need to be travelling at the illegal speed 0.5 seconds before reaching the end of the road markings so that the two photographs occur within the road markings.
Anyone good at maths?
But the question was "can you get one to trip from a standstill?"
F1 cars are s
t at standing starts. They are not optimised for them.
I have seen a Subaru Impreza get one flash from a scamera from a standing start. I imagine this is because he ran out of markings before the second flash would have gone out.
Yes it can be done in a fast road car.
F1 cars are s
t at standing starts. They are not optimised for them.I have seen a Subaru Impreza get one flash from a scamera from a standing start. I imagine this is because he ran out of markings before the second flash would have gone out.
Yes it can be done in a fast road car.
Vipers said:
Petrolhead_Rich said:
Vipers said:
Formula 1 perhaps? Just guessing.
According to Top Gear Tests a "Reasonably Priced Car" (Lacetti) is faster than an F1 car off the line! Anyone remember the tests they did (in the Birmingham NEC IIRC)It defiantly happened though and the normal car won!
Petrolhead_Rich said:
Vipers said:
Petrolhead_Rich said:
Vipers said:
Formula 1 perhaps? Just guessing.
According to Top Gear Tests a "Reasonably Priced Car" (Lacetti) is faster than an F1 car off the line! Anyone remember the tests they did (in the Birmingham NEC IIRC)It defiantly happened though and the normal car won!
er, surely, it depends on how far away you start?? Assuming the camera measures your speed "just" before you cross the first line, then if you are not speeding at this point,further accel in the zone between the "verification" lines makes no difference. Pretty fast "normal" cars can accel just about 1g for a short distance, which means over 30 would take 1.4sec and take 9.2m. So to be in any hope of tripping even a "30mph" camera, you'd have to start at least 2 car lengths away from the line!
Max_Torque said:
er, surely, it depends on how far away you start?? Assuming the camera measures your speed "just" before you cross the first line, then if you are not speeding at this point,further accel in the zone between the "verification" lines makes no difference. Pretty fast "normal" cars can accel just about 1g for a short distance, which means over 30 would take 1.4sec and take 9.2m. So to be in any hope of tripping even a "30mph" camera, you'd have to start at least 2 car lengths away from the line!
For a more normal car, mean accel will be closer to 0.5g (in 1st gear) and the camera will probably require 35mph to actually trigger (in a 30mph limit) this needs 3.2s of accel from rest, taking 25m distanceI'm not going to do the differential calculations to get an exact value, as I can't be arsed, so I'm assuming the gatso trips at 35mph and that if you reach 37mph by the end of the 32m. I'm also assuming uniform acceleration. Round up 37mph to 17m/s
Some basic calculations, using
a = ( Vf - Vi ) / t
and
d = (( Vf + Vi ) × t )/2
t= 2d/(vf-vi)
a= (17-0)/t
:. a= 4.5 m/s/s
So to reach 37mph from a standing start in 32m would require the acceleration of 4.5m/s/s.
That equates to a 0-100kph time of:
a=(vf-vi)/t
t=(vf-vi)/a
time = (17)/4.5 = 3.7
So theoretically, a car with a 0-60 time of 3.7s could trigger a Gatso in a built up area.
Feel free to tear my schoolboy physics to shreds
Some basic calculations, using
a = ( Vf - Vi ) / t
and
d = (( Vf + Vi ) × t )/2
t= 2d/(vf-vi)
a= (17-0)/t
:. a= 4.5 m/s/s
So to reach 37mph from a standing start in 32m would require the acceleration of 4.5m/s/s.
That equates to a 0-100kph time of:
a=(vf-vi)/t
t=(vf-vi)/a
time = (17)/4.5 = 3.7
So theoretically, a car with a 0-60 time of 3.7s could trigger a Gatso in a built up area.
Feel free to tear my schoolboy physics to shreds
But, the "speed sensing" is either inductive loop or radar, either of which operate in the zone BEFORE the camera, and must be tripped to start the 2 photo recording process. if you haven't tripped it as you cross the first line, then you can go as fast as you like towards the second line
Max_Torque said:
But, the "speed sensing" is either inductive loop or radar, either of which operate in the zone BEFORE the camera, and must be tripped to start the 2 photo recording process. if you haven't tripped it as you cross the first line, then you can go as fast as you like towards the second line
One way to find out is to find a front facing camera and someone with a motorcycle 
Petrolhead_Rich said:
Vipers said:
Petrolhead_Rich said:
Vipers said:
Formula 1 perhaps? Just guessing.
According to Top Gear Tests a "Reasonably Priced Car" (Lacetti) is faster than an F1 car off the line! Anyone remember the tests they did (in the Birmingham NEC IIRC)It defiantly happened though and the normal car won!
They said afterwards if they hadn't bothered with the F1 car they'd have held the world indoor speed record with a Chevy!
Edited - my memory had a Skoda in it, but found the vid and it was the Chevy.
http://www.youtube.com/watch?v=2uG9Afp6fy0
Edited by john2443 on Monday 10th January 17:54
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