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paulqc

Joined:

Jun 09

Posts: 30

paulqc says:

Speeding

Hi, can anyone help?

This morning I was stopped by Plod for sppeding.  The officer was using a hand held SL700 device, and clocked me at 68mph within a 50 zone.  I had just over taken a transit van and both me and the guy who was riding behind me are certain that our speed was not above 55mph.  The officer was not interested in our argument, and insisted in giving me a ticket worth three points and £60. 

I'm not sure, but I have a vague memory of this error in recording speeds using hand held devices has been written about, and proved that there can be errors with the units.  Does anyone remember this, or have any info relating to wriggling out of this type of situation?

 

Thanks,   Quig.

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  • Posted 5 years ago (25 April 2010 11:30)

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triumphrider600

Joined:

Feb 09

Posts: 550

I believe

that the error rate is due to 'slippage'. These devices ideally need a flat surface to point at, i.e. the front bumper of a car, for the laser to rebound.

Bikes do not normally offer such a surface and 'can' distort readings. Some hand held devices have recorded 30+ mph speeds of stationary walls in court rooms.

You will need to contact a motoring lawyer for expert advice. There are a couple that post on here so maybe they will respond to you direct.

 

Good luck,

Tom

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paulqc

Joined:

Jun 09

Posts: 30

paulqc says:

Speeding part deux...

I've discussed the sppeding event with my friend, who was with me at the time. Having discussed the matter at length, I am convinced that we were not speeding, not to the extent that the SL700 recorded anyway.  Armed with this conviction I telephond several Legal firms to seek advise on the matter. Every one of them agreed with me that the reading was probobly inaccurate, and that the chance of fractured dopler being recorded by the device, rather than the true return was a near certainty. This could be fought in court, with many accounts of such inaccurate claims by the various constabularies using the same device, but I'll need to pay a minimum of £2k up front for them to start the challenge.

So I'll take the £60 fine and three points. I'll also be writing to my MP in disghust. This is a huge shit sandwhich, and I'm having to take a great big bite out of it.

Not happu at all.

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GrumpyPixie

Joined:

Apr 06

Posts: 30

GrumpyPixie says:

Have I misunderstood?

You were caught doing 68 but are certain you were doing just 55? If this is the case and the limit was 50, you were still speeding so should still expect 3pts and a £60 fine.

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philehidiot

Joined:

Feb 09

Posts: 4683

philehidiot says:

Lol

Doppler is a very, very sensitive beast.

There are three main ways of getting errors:

1) You must be in line with the direction the target is moving in order to get an accurate velocity measurement. The element of the equation is COSθ (θ = angle between your line of sight and the actual direction of travel). COS90 is zero, so the more out of line you are, the greater the error. This error always reduces the velocity and is in your favour.

2) Overshoot - scraggly crap around the top of the Doppler trace. It takes experience of looking at a Doppler signal to differentiate between overshoot and an actual peak velocity. I would not trust a machine to do this accurately. Sometimes to make the trace clear, you have to play with gains, post processing and the colour scheme of the graph to make it more readable. In medicine we never trust a machine to automatically trace a Doppler signal.

3) Angle of the surface - as you say, it needs a flat surface that is not angled or anything to allow the beam to bounce back to its point of origin. If it doesn't, then you'll get scatter and the trace will be bullshit. This is how radar invisible bombers work, by not having right angles and so, in conjunction with radar absorbent materials, the beam is absorbed and scattered rather than returned to the source.

I have spent ages staring at and playing with Doppler traces when I've had half an hour acquiring the perfect signal. I would not trust someone to acquire, using a hand held piece of kit, an accurate peak velocity, with a clean signal that can be easily measured by a computer on a target moving at 8m/s (30mph), never mind 68mph. Given the range (bear in mind a 1 degree wobble at the source is going to be a massive wobble at a distance), the size of the target (a numberplate) and the speed, not even a qualified marksman or army sniper could be expected to make that shot reliably.

I'm sorry but just basic physics and experience of shooting things tells me that the manufacturers of these things are playing on people's ignorance and not being honest about their limitations. I'm sure the police use them in good faith however, they're not going be trained to understand the physics involved and therefore the limitations of the readings they acquire. I feel that the machines should record the exact trace and that this should be submitted, alongside the video, for analysis by a trained person before a fixed penalty can be delivered. It would take maybe 5 mins per ticket to say if something is reliable or not. The current system relies on a computer to make sense of data collected in imperfect circumstances and is used to criminalise people on the spot.

EDITED to stick the theta symbol in properly.

[This Reply has been modified by the Author]

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paulqc

Joined:

Jun 09

Posts: 30

paulqc says:

GrumpyPixie

I don't believe you have misunderstood GrumpyPixie, you just appear to be ignoring the obvious.  Yes, I was speeding, perhaps by as much as five miles per hour (shock horror).  This has been agreed by the friend with whom I was travelling with at the time.  That being true, and if we're drawing a easily identifyable line between being on the wrong or right side of the speed limit for any given road, then I'll take my three points and sixty ponds fine with good grace.  The fact is that all Police Officers are obliged to use discression, as a professional action to determine the nature and severity of the individual offence, are they not?  In this case that process was removed and replaced with what is obviously a inaccurate method of detection.  If the Officer had determined that my speed was only just above the 50mph limit, I'm sure a stern word would have sufficed, and would have been taken at it's face value.  My objection is that we, as the Motorcycling public are expected to accept that this machine is infalable, and the reading given is beyond question, as such my ability to persue justice is mightly diminished. I find that imoral and unacceptable, given that in all legal precidents in this country, all extenuating circumstances are considered before any punative action is implemented is it not?  Where was the consideration is this situation, even after both parties travelling had objected to the measured speed, do I not have the right to question this process?

  I believe I do have that right, especially when the reading is obviously so inaccurate.  As a former Royal Navy electronics Engineer for fourteen years, I understand the engineering process, the physics and deviation of Dopler return, and it's easy to see that this method of speed detection is unsafe for Motorcycles.  Also as a former member of the Armed Forces I have actively fought, and very much risked my life on occasions, to maintain the right of freedom and justice.  So, I must thank you for your input into this thread, but insist that you stick it up your arse.

Thank you.   

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Fazerpod

Joined:

Mar 06

Posts: 262

Fazerpod says:

55 on the speedo

55mph in a 50 zone should be perfectly OK on most speedos.

My husband & I did bikesafe a few years back and the plod who took us out (who was the senior biker for Kent & Sussex) told us that both our speedos were 10% out and that we needed to ride faster!  He took us out to "calibrate" our speedos against his and we were OK to do 10%  over in each speed range.

That's on a Yam Fazer and a Kwak ZX6R.

I follow the same principle in my car too (backed up by GPS device) and so far I've not had a ticket from the cameras on the M3

Sorry about your bad luck Quig, if I were you I'd do the same - shame really since the system needs someone to fight it :mad:

[This Reply has been modified by the Author]

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GrumpyPixie

Joined:

Apr 06

Posts: 30

GrumpyPixie says:

Speeding

The fact that the detection equipment is flawed is not the issue. And getting a ticket is certainly not down to bad luck. If you don't want a ticket don't break the speed limit.

The police are not obliged to use discretion at all. You, on the other hand, are obliged to obey the speed limit and all the other traffic laws. You wouldn't expect to get away with running a red light using the defense 'It was only a couple of seconds after the lights changed.'

The fact remains that if you were travelling at 50 you would not have been pulled and therefore you only have yourself to blame. It is time you grew up a little and took responsibility for your actions, and your comment about my arse is just further evidence your childishness.

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bbstrikesagain

Joined:

Nov 08

Posts: 878

Fazerpod

Slightly dangerous advice.  In general speedos by design (assuming you haven't changed the gearing or tyre size) read about 4% to 6% over.  The legal limit is 0% to 10%, so all speedos are initially targeted well away from those values.

So, with a reading of 10% over, most people would actually be around 5% over the limit - well within the ACPO guidelines, but speeding nonetheless, so you could, in theory, still be prosecuted.

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Anonymous

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Anonymous  says:

Speeding!

Should have gone flat out so the fuckers couldn't even get a reading! xD

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Anonymous

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Anonymous  says:

Speeding!

Should have gone flat out so the fuckers couldn't even get a reading! xD

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