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Governor312
Ok a stuipid question i guess but how do the Specs cameras work out your speed? For example if i was going round M25 where there are quite a few of these cameras operating with a 50mph speed limit, what sort of tollerance do you have going through them, is it the normal 10% +2? Also if i drove through them at 50mph is this my average speed between the points, as i understood that was not the case, but maths beats me every time!!! mellow.gif
Mortimer
Simple maths, distance over time.

The computer system knows how far apart the cameras are. Using ANPR your car is timestamped at each camera. The distance between a camera pair divided by the difference in timestamps gives an average speed between the two cameras. If this is over the speed limit, bingo, one NIP on its way.
nemo
Drive through Camera A, VRM is scanned and timestamped.

Drive through Camera B (which is a known distance from Camera A), VRM is re-scanned and re-timestamped.

Basic S=D/T calculation allows average speed to be determined between the two fixed points.

I am not aware of any SPECS installations which have resulted in NIPs being issued for speeds less than 10% plus 2mph in excess of the posted limit.
Governor312
QUOTE
I am not aware of any SPECS installations which have resulted in NIPs being issued for speeds less than 10% plus 2mph in excess of the posted limit.



So i drive M25 route everynight with the 50mph roadworks, in my work as a trucker, my truck is limited to 56mph, although Satnav says 54, so i am below the 10% +2 margin if i carried on with this speed? Also am i correct in saying that most speedos ore not actually correct, ie the differance between my speedo readout & satnav speed??
Mortimer
Speedos will only ever over read. They won't under read your speed unless there is fault somewhere. Typically they are high my 2 or 3 mph.
nemo
QUOTE (Governor312 @ Fri, 14 May 2010 - 15:43) *
So i drive M25 route everynight with the 50mph roadworks, in my work as a trucker, my truck is limited to 56mph, although Satnav says 54, so i am below the 10% +2 margin if i carried on with this speed?

Whilst a true vehicle speed of 54mph is likely to be below the enforcement threshold, it would be no defence to an allegation of excess speed to state that 'some bloke on the internet told me.....'.

QUOTE (Governor312 @ Fri, 14 May 2010 - 15:43) *
Also am i correct in saying that most speedos ore not actually correct,

The size of error is likely to vary from speedo to speedo. But it's worth noting that speedometers must not display a speed which is lower than the true vehicle speed.
Governor312
Thanks everyone for your helpful advice
dom
QUOTE (nemo @ Fri, 14 May 2010 - 15:55) *
QUOTE (Governor312 @ Fri, 14 May 2010 - 15:43) *
So i drive M25 route everynight with the 50mph roadworks, in my work as a trucker, my truck is limited to 56mph, although Satnav says 54, so i am below the 10% +2 margin if i carried on with this speed?

Whilst a true vehicle speed of 54mph is likely to be below the enforcement threshold, it would be no defence to an allegation of excess speed to state that 'some bloke on the internet told me.....'.

QUOTE (Governor312 @ Fri, 14 May 2010 - 15:43) *
Also am i correct in saying that most speedos ore not actually correct,

The size of error is likely to vary from speedo to speedo. But it's worth noting that speedometers must not display a speed which is lower than the true vehicle speed.




Should that read "must display" rather than "must not display"?



Dom
nemo
QUOTE (dom @ Fri, 14 May 2010 - 21:52) *
QUOTE (nemo @ Fri, 14 May 2010 - 15:55) *
But it's worth noting that speedometers must not display a speed which is lower than the true vehicle speed.

Should that read "must display" rather than "must not display"?

As in, a speedometer 'must display' a speed which is lower than the true vehicle speed ?

Err, no..
dom
QUOTE (nemo @ Fri, 14 May 2010 - 22:00) *
QUOTE (dom @ Fri, 14 May 2010 - 21:52) *
QUOTE (nemo @ Fri, 14 May 2010 - 15:55) *
But it's worth noting that speedometers must not display a speed which is lower than the true vehicle speed.

Should that read "must display" rather than "must not display"?

As in, a speedometer 'must display' a speed which is lower than the true vehicle speed ?

Err, no..




I may be being rather dim here..... smile.gif But "it's worth noting that speedometers must not display a speed which is lower than the true vehicle speed" cannot be correct as they all do?
If it said higher rather than lower I'd agree!


Dom
bama
Its easier with out the boolean stuff.

speedos must over read i.e. they show a higher speed than the actual speed.

andy_foster
QUOTE (dom @ Fri, 14 May 2010 - 22:24) *
I may be being rather dim here..... smile.gif


You may say that, but I couldn't possibly comment...

QUOTE
But "it's worth noting that speedometers must not display a speed which is lower than the true vehicle speed" cannot be correct as they all do?
If it said higher rather than lower I'd agree!


Imagine that you're driving on a restricted road - 30 mph speed limit. Imagine that you speedometer is displaying a speed of 30 mph. Assume that your speedometer is not accurate. Lets assume that you are correct and that speedometers must not display a speed which is higher than the true speed, but may display a speed lower than the true speed. If the speed displayed is 30 mph and it is lower than the true speed, your true speed is higher than the speed limit which your speedometer tells you you are complying with, but you are actually breaking the law. Is that what the C&U regs are all about?
metalmick
We have a length of the M62 nr leeds with about 6 sets of specs cameras, by what you are saying I could speed between alternate pairs and get a ticket for each occasion?
As it happens I tend to hold to 50-55 in the 50 limit area but was under the impression that speed was calculated over the length of the controlled area you were driving, ; if I drove at say 50 for 5 pairs of cameras but went up to 60 say for the distance between 1 pair would that result in a ticket.
mike
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