Speed camera calibration

born_again

SephiaBB said:

My wife was recently sent a notice of intended prosecution for speeding. We have gone online to the police website. However when we try to access and look at the camera calibration certificate we get a message saying it is not available and may have been removed. We sent a query via the online form, requesting access to the certificate but received no response. Obviously there is a time limit for our response. Of course we have no evidence of our speed. The speed limit was 40mph, the prosecution notice states we were doing 46 mph. 
My query to the forum is how do we stand regarding the calibration certificate not being available? 
Thanks

What sort of camera?
Fixed or mobile.

Car_54

born_again said:

SephiaBB said:

My wife was recently sent a notice of intended prosecution for speeding. We have gone online to the police website. However when we try to access and look at the camera calibration certificate we get a message saying it is not available and may have been removed. We sent a query via the online form, requesting access to the certificate but received no response. Obviously there is a time limit for our response. Of course we have no evidence of our speed. The speed limit was 40mph, the prosecution notice states we were doing 46 mph. 
My query to the forum is how do we stand regarding the calibration certificate not being available? 
Thanks

What sort of camera?
Fixed or mobile.

And the difference that would make?

Grey_Critic

Back in the 1980s we were contacted by the local authority re a speeding ticket one of their employees had received. Was it possible to confirm the accuracy of the speedometer as the driver was adamant that he had not been speeding.

We were a Tachograph Centre with a rolling road and the necessary equipment so yes no problem. On test we found the speedometer was incorrect by 6mph. This was due to wear on the speedo drive.

Not sure how the speedo pickup is done these days but it is possible that the OP was driving at 40 mph according to the in-car reading but was in fact exceeding the posted limit.

Car_54

Grey_Critic said:

Back in the 1980s we were contacted by the local authority re a speeding ticket one of their employees had received. Was it possible to confirm the accuracy of the speedometer as the driver was adamant that he had not been speeding.

We were a Tachograph Centre with a rolling road and the necessary equipment so yes no problem. On test we found the speedometer was incorrect by 6mph. This was due to wear on the speedo drive.

Not sure how the speedo pickup is done these days but it is possible that the OP was driving at 40 mph according to the in-car reading but was in fact exceeding the posted limit.

If the speedo was indeed under-reading, that in itself is an offence.

Nasqueron

Grey_Critic said:

Back in the 1980s we were contacted by the local authority re a speeding ticket one of their employees had received. Was it possible to confirm the accuracy of the speedometer as the driver was adamant that he had not been speeding.

We were a Tachograph Centre with a rolling road and the necessary equipment so yes no problem. On test we found the speedometer was incorrect by 6mph. This was due to wear on the speedo drive.

Not sure how the speedo pickup is done these days but it is possible that the OP was driving at 40 mph according to the in-car reading but was in fact exceeding the posted limit.

Speedos are always set to over-read by 1-2mph though legally can do so by as much as 10%+6.25mph, they cannot, by law, show you doing less than the speed - anyone doing 46mph would likely see 48-50 on the speedo, almost certainly OP wife thought she was in a 50 limit and was just under for safety but was actually speeding in a 40

Grey_Critic

Wear on the pickup will effect the reading -

SephiaBB

Thank you everyone for your useful comments. Yes my wife had receive the notice of prosecution. We realise the the most economical route is probably to accept what's coming -- hopefully the offer of a course. As someone who works in measurement it did annoy me somewhat the they post up a calibration certificate and then apparently remove it -- I had previously queried this with the online form with reply, hence the use of we in my post here.
Many thanks again everyone

Nasqueron

Grey_Critic said:

Wear on the pickup will effect the reading -

Yes it will - but it's very minor and of course, it actually reads down - an example I found here on stack exchange  in the mechanics section said a drop from 10/32" to 2/32" (yes it's American example) would give just 2% error - that is in part why they always set them to over-read the speed so you cannot have a situation where a car is showing say 40mph and doing 45mph - there is an example at the bottom where someone put smaller wheels on their motorbike (equivalent to extreme tyre wear!) and the speedo shows 40mph when the GPS shows 35mph

Overinflating can also make it read slightly higher too - a bigger wheel (overinflation would increase the diameter for example) would cause it to go up 

Another example is here on reddit where an F1 team looked at this, 0.6mm tyre wear on the tyre dropped the speed from 80kmph to 79.87kmph on the pit limiter and it's calculated 79.4kmph with 2.5mm tread gone

forgotmyname

If the ticket said 46mph the actual speed would have been higher. They already deducted a set amount to avoid the cases where its
so close that the calibration comes into it.

At least another 2mph if they put 46mph the actual speed would have been at least 48mph.

[Deleted User]

Unfortunately, unless you have evidence that you were not speeding, like GPS logs or a dashcam that shows your speedometer, you are screwed.

The court won't care about missing certificates, they will assume the speed camera is infallible. The normal "beyond reasonable doubt" standard doesn't apply in practice.

Give up and ask for the course, and buy yourself a GPS dashcam.