Safe Speed Forums

Thing is, in this case what would it show?
In a case of slip: it would not show anything (which is why the gun can be fooled) – this being hugely more significant than interference from posts and such.

If a lamp post got in the way for part of the time you would see a sudden decrease in the distance and then a sudden increase as the laser hit the post and cleared it again. It would be obvious that *something* was wrong even if you did not know what until you analysed the data.

I'm not sure what the raw data would show in the case of slip, but I know from work I have done with other equipment (nothing to do with speed cameras!) that you can discover all sorts of interesting things once you have access to *all* the data.

Yes, but what would the point be if the device already has an error code for such a case (should it become significant) and such interference cannot lead to a false speed reading?


Nothing.
The front end is very basic; it simply reduces the received light into a simple single bit digital pulse train for use within the timing modules. The pulse train will not be any different in the event of a smooth surface sweep; hence the data cannot indicate that anything is amiss - that's why the gun is fooled.

Make that: That's why the flaws are fatal.

No instrument which works on such a principle can be made safe from the possibility of slip effect. No system of error detection can ever detect all cases of slip. And that means that the evidence of the gun cannot ever be 'beyond reasonable doubt'.

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Paul Smith
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The Safe Speed campaign demands a return to intelligent road safety

I made a diagram in OpenOffice Drawing Format but I also exported it as a PDF.

The drawings are not to scale.
The numbers are made up, but should be somewhat 'real'...?

Does this look right to show how the device can't tell the difference between movement of a vehicle and slip?

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Andrew.