Safe Speed Forums

Shout it from the rooftops.
This is disgraceful.

What I find really objectionable, is that Joe Public who is driving safely and responsibly and within the limit is threatened with extra sanctions if he/she contests the charge and fails.
This is nothing short of state bullying.

All the evidence should always be readily available to the charged person. From the moment the envelope falls on the doormat the system is biased against the charged person, who would not normally have sufficient technical knowledge to dispute the charge except for a "gut feel" but is pressurised by the system to accept that the technology/authorities are right and the accused is wrong.

This is bad.

Sorry Guys,

I've been working on this one for a week and I haven't announced it in here. In the first place the BBC guys asked me to keep quiet because they were trying to make a news splash, but when the brakes came off yesterday I should have posted something here in a public forum.

Safe Speed sent the following PR at 11:50 yesterday morning:

PR175 BBC will reveal laser speed meter errors

News: strict embargo: 7.30pm Monday 28th February 2005

This evening at 7:30pm BBC South West TV programme: 'Inside Out' will
demonstrate erroneous readings from a Home Office approved laser speed
meter. Safe Speed has long been extremely concerned about erroneous
readings from laser speed meters.

Two important examples to be shown in the programme are

* measuring the speed of a brick wall at 58mph
* measuring the speed of a stationary car at 4mph.

Paul Smith, founder of the Safe Speed road safety campaign
(www.safespeed.org.uk) said: "We hear many complaints from motorists
who do not believe the laser speed meter reading that is being used
against them. Unfortunately it is extremely unusual for a motorist to
be able to offer alternative legal evidence of their speed at the time
of the alleged offence. We are certain that there are many thousands
of cases where motorists have been wrongly convicted due to faulty
evidence from laser speed meters. It's quite possible that all laser
speed meter convictions are 'unsafe'."

Safe Speed demands that Home Office approval for laser speed meters is
suspended immediately pending a full investigation.

"It's not as if high levels of speed enforcement are making the roads
safer." explains Paul, "Road safety absolutely depends on speeds
selected by drivers as being safe and appropriate for the immediate
conditions. High degrees of speed enforcement are leading to an
increase in unsafe speeds as some drivers trust the number on the sign
instead of the evidence of the road ahead."

A recent case in Inverness Sheriff Court was dismissed after a laser
speed meter recorded a speed of 132mph from a vehicle that was proved
not to be capable of exceeding 107mph.

<ends>

Notes for Editors
=================

BBC Inside Out web site:
http://www.bbc.co.uk/insideout

BBC Inside Out South West web site:
http://www.bbc.co.uk/insideout/southwest

BBC web page for this programme item:
http://www.bbc.co.uk/insideout/southwes ... eras.shtml

BBC1 South West is available out of area on Sky Digital Channel 957

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I had to smile when the Beeb described the NFG20-20 Dodgyscope as "one of the latest guns used by the police". Funny how the manufacturer said it supposed to know when it's being panned and would display an error reading instead of a speed, but failed to explain how the Beeb managed to clock a wall at 58mph by panning one. To me that suggests that whatever is fitted to it to detect panning doesn't work.

_________________
Make everything as simple as possible, but not simpler - Einstein

Of course we are getting dads army using these now. Wait till we get a Punto clocked at 270mph....

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Speed camera policy Kills

It occurred to me that the only way to eliminate 'slip' angle and reflection error when using one of these devices would be to place the gun (and the operator ) directly in front of and at the same level as the vehicle..

New operational guidelines - ping the car and then get out of the way quickly!!

Hehe! - but even that doesn't work. It could still slip from numberplate to roof line, and it could still double bounce off something brightly reflective on the vehicle.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I just suggested pretty much the same thing as r11co in the other thread - great minds etc . I've given it a bit more thought and I reckon they can avoid the double bounce if they choose the site carefully, and there's still a solution to the problem of the laser slipping from plate to roof. It's really easy actually - the operator would have to lie on the road and remain very, very still .

_________________
Make everything as simple as possible, but not simpler - Einstein

A biker mate of mine was nailed by the Soverign Base Area Police in Cyprus doing 80kph in a 60 limit. He swears he was doing 60 and contacted someone in the UK who told him that, apparently, certain types of hand held guns can be fooled by the speed of a rotating spoke, particularly a large alloy one, on a bike. An advancing spoke would naturally produce a high speed reading..
Anyone heard this before?

Yes. Never seen it proved.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I'm guessing that the more likely primary route of return would be a double-reflection from spoke to inside rim back to the gun (or the other way around), with several secondary possibilities via other reflective surfaces as a result of the double reflections sideways (spoke and/or rim being convex).

I've just been thinking about this (admittedly light-hearted) article regarding the spurious readings from a particular radar gun.

I remember reading years ago how in particular GRP bodied cars could present difficulties for radar guns to get speed readings as radar waves pass through plastic (with an amount of absorption) rather than being reflected.

The instance of the Hoover mentioned above could be quite easily explained by the radar waves penetrating the casing of said vacuum cleaner and measuring the speed of the motor within!

The tree baffles me though - slip error?

The spoke thing sounds absolutely reasonable to me.

If you are stood in front of an approaching motorcycle, then the spokes in the top half of the front wheel are advancing towards you at up to twice the speed of the bike (depending on how far up from the centre of the wheel you are looking).

Of course you can't see them for the tyre, but if you were to be slightly to one side of the path of the bike (eg sat in a van at the side of the road) then the spokes would be visible. A typical cast alloy wheel tends to have a small number of relatively large section spokes, so it seems very plausible to me that there could be a significant amount of "returned beam" from the spokes, and of course the nearer the bike gets the higher the percentage of the beam that could be returned.

If the laser / radar gun works by picking up an "average" returned beam from the target vehicle, then it seems very possible that the apparent reading could be increased by a variable amount, anywhere up to double the actual speed.

It would be very interesting to do an experiment with a static motorcycle sat on its stand, weighted so that the front wheel is off the ground. Then spin the front wheel and see what speed measurements could be taken fron it with a laser gun, and at what ranges.

Of course if this is true, there is also no reason why the same effect wouldn't happen with car wheels, especially given the current trend towards large pattern alloy wheels with ultra low profile tyres.

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CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

Just as a bit of a visual cue, here's a piccie of my car (taken just before I washed it the other week but that's another story! )

Imagine it is driving away from a "talivan", and the operator has the beam patch focused where the red circle is. Look carefully at the profile of the spokes. How fast will they be receding from the camera, and what "average" reflection will the gun take?



The way I see it, the "edge" of the spoke is about the only thing in that circle that would provide any sort of reflection back to the gun...

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

The way I see it there will be no coherent return to the laser device as a direct result of your wheel turning and as the acceptance angle is very small . The gun will not see some of the returns so indicates an error. No speed measurement is obtained. You see how easy it is to start off a rumour when you have a little knowledge of the gun and make assumptions.
A bit like that fella on the BBC on Monday.

Thanks for your time putting that together JJ.

What is the pulse frequency of the Lti20-20 then?

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

Oh I do despair. Are you trying to work out the wheel rotational speed and angular displacement of the beam? Just work out the radial speed of your spoke and work out how it would change the angle in a radians/second measure for a range of speeds. A man of your calibre will find no problem with that I'm sure. Excel will aid you as it defaults to radians. Crack on and let me know what you get.

The Pulse Repetition Frequency wil be confidential to the distributor. I can't release it.

Take my word for it, the wheel spokes will cause an error that prevents a speed reading.

Can confirm the geometry side of it poses no insurmountable problems (I used to write CAD software!)

No, I was looking at it a little more simply than that. Looking in my theoretical "beam pattern circle" the only object I can see that would be likely to reflect any of the beam back to the gun would be the edge of the spokes.

My understanding is that the Lti20-20 measures speed by comparison of repetitive range measurements of the same target object. Is that correct? Assuming it is, then if I knew how far apart the pulses were I'd be able to decide how far any specific spoke would have advanced during that interval, and therefore whether the unit would be able to get two (or more) coherent range measurements from the same spoke before it rotated out of view. If it could then it could get an apparently sensible speed reading from it, and moreover this would be continuous as a "new" spoke keeps coming into view and establishes a fresh set of returns to replace the ones lost as the last spoke rotates out of view.

In fact, I would even go as far as to propose that it's not a question of whether the spokes can provide a reading or not, but merely under what set of speeds and camera ranges.

I'm sure you will agree that if you stood a couple of feet away and put a pinpoint beam onto one spoke of a slowly rotating wheel then you'd get a speed reading, even if the wheel was rotating jacked up on a stationary car. As you increase the speed of the wheel you will presumably reach a certain point where the pulse frequency is no longer fast enough relative to the speed of the spokes to be able to acquire a reading. Similarly, if you increase the camera range then you will reach a point where the size of the spoke is no longer influential enough to affect the gun, relative to the size of it's field of view.

I was just curious to see what sort of numbers these would be, and I would have initially expected that the "cutoff" speed / range would be pretty low, but recently reported events seem to be indicating that this sort of thing might perhaps be a problem after all...

(And your reticence is doing nothing to reassure me JJ )

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

The Lti 2020 issues laser pulses at 125Hz.

Your could possibly measure a valid speed from advancing spokes because the thing doesn't measure speed. It calculates speed from a 'ramp' of distance measurements. You'll quite possibly get a ramp from advancing spokes, but the speed would be true.

You can't say that for doppler radar.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

JJ, as you should have a better working knowledge of the guns I'd like to hear your comments on the panning or slip error. The BBC say they got a 58mph reading off a wall this way, but Frank Garrat said the device detects slippage and returns an erorr reading. Any idea why this did not happen when the Beeb tried it? There seems to be two immediate possibilities - first, that the detection of slippage isn't anything like as reliable as Tele-Traffic thinks and would have us believe, or second, that bad handling on the part of the operator can overwhelm the ability of the device to detect slippage.

IMO either should be cause for concern over the use of these guns. If the slippage detection is unreliable the there is not only the possibility of unfair prosecutions resulting from over reads, but also missing speeding drivers if the guns can also under read. In other words, not only might it catch the innocent, it could also fail to catch the intended targets. The same applies if it is due to operator error. If the guns are to be used as they are there must be absolutely no question of their reliability, not just in themselves but as used by an operator who may be having an attack of the clumsies one morning.

Or can you offer a third possibility for the 58mph wall reading that doesn't question the reliability of the gun or its operation?

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Make everything as simple as possible, but not simpler - Einstein