Safe Speed Forums

The Sheffield Star
http://www.thestar.co.uk/news?articleid=3093217

Slower than the speed of light



Speeding appeal: Iain Fielden


A UNIVERSITY lecturer from Sheffield is trying to use the laws of physics to help his wife escape a speeding fine.
Dr Iain Fielden, who lectures at Sheffield Hallam University’s Materials and Engineering Institute, claims the whole science behind the way speed cameras operate is flawed.

And, if he and his wife Vikki win an appeal, they could change the way speeding fines are dished out right across the country.

Mrs Fielden, aged 48, was flashed in July last year as she drove along the A616 at Brockholes in West Yorkshire.

The prosecution claim she was driving too fast - at 36mph in a 30mph zone - and she was convicted at Huddersfield Magistrates’ Court of speeding.

But Dr Fielden, of Shirecliffe Road, says the way speed cameras collect information is unreliable - and could be needlessly convicting thousands of people.

He set out to prove that, because his wife’s car was rounding a bend at the time it was flashed, the information transmitted by the radar would not be the same as if the car was on a straight section of road.

Dr Fielden - who conducted his wife’s defence in court himself - says the magistrates accepted his findings, but convicted his wife anyway after hearing other evidence. The couple now plan to appeal.

Dr Fielden said: “They accepted it in court. But they convicted on the secondary evidence of marks on the road and two photographs.

“That shouldn’t have been presented as the only evidence. Secondary evidence should only be used as back-up to the main evidence, not as the central evidence itself. But she was found guilty anyway.”

Mrs Fielden was fined £100, ordered to pay £200 costs and given three penalty points.
Last Updated: 08 August 2007 7:45 AM

Hmm, those non-biased magistrates at work again.

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Paul Smith: a legend.

"The freedom provided by the motor vehicle is not universally applauded, however: there are those who resent the loss of state control over individual choice that the car represents. Such people rarely admit their prejudices openly; instead, they make false or exaggerated claims about the adverse effects of road transport in order to justify calls for higher taxation or restrictions on mobility." (Conservative Way Forward: Stop The War Against Drivers)

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Andrew.

I don't understand what the problem is, could someone explain?

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Erm... <insert really complicated maths>

Basically the bend will have an effect on the recorded speed. I think bending towards the camera decreases the apparent speed, bending away increases it. (I may of course have those the wrong way round)

I remember reading somewhere that the Gatso radar unit must be mounted at 90° to the road and not on a bend. This may be in the type approval or user manual. If it is then the maths isn't even needed.

I don't know that this is a Gatso though, but the only other radar units I know of are hand-held and aren't used very often. Physics still applies.

I have found the interesting Thread on PePiPoo where this was all explained.

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Andrew.

Its just a guess, but could it be that if the beam is returning from the side of the car as it turns towards the radar head then the angular speed of the car is added to the linear speed? Sounds unfeasible, and can't see it making more than a couple of mph difference, but its the only thing I can even imagine.

It only needs ONE mph difference to be convicting people incorrectly though...

Cheers Andrew. That 20 degrees cosine error bumpf makes sense.

For those who want a summary:
the radar unit is approved for use set up to 20 degrees away from the direction of traffic; the radar unit cannot be placed exactly in line with the direction of traffic – for obvious reasons
I guess they 20 degrees was chosen for practicality (minimise depth of sensor zone) without adding too much of a 'fudge factor'. This angle of operation means the speed detector will always underread, resulting with it giving 94% of the actual vehicle speed (just like an LTI2020 would if used at that angle - the cosine effect). The good people at Gatso added the fudge factor of +6.4% to compensate for this underread. This works well if the target vehicle is travelling at the 20 degrees from the angle of the beam; it doesn’t work so well if the vehicle is travelling directly in line with the beam - like when on a bend where a true 30 would be read as 32; that would already be 66% of the allowable tolerance used up.

Excellent!
I'm a bit too tired to understand it at the moment, fortunately not too tired to find that link.

Of course at 36mph even 1mph less would have probably not triggered the camera.

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Andrew.

All they need to do is prove that you were exceeding 30mph. It doesn't matter if you were doing 31 or 36 the offense has still been committed.

That is true, the issue is proving it. (Un)fortunately, radar speed meters are notoriously dodgy.
For a gatso, I believe the secondary reading must be within 10% of the primary for the prosecution to stand, otherwise the equipment will be deemed to be faulty. The lower of the two readings is used for the prosecution.

The following link is self-explanatory and I would welcome comments on the DVD frames, which are "TIMEOUT"

http://iwillbthere.co.uk/speedcameras.aspx

I most certainly was NOT speeding.

Apparently they also measured the radius of the bend in feet and not meters as it should have been.

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Useless laws weaken necessary laws.