RE: BBC demonstrates lasergun errors
Tuesday 1st March 2005
BBC demonstrates lasergun errors
Campaign demands withdrawal of faulty equipment
Last night, a BBC South West TV programme: 'Inside Out' demonstrated 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 shown in the programme are:
- Measuring the speed of a brick wall at 58mph
- Measuring the speed of a stationary car at 4mph.
Founder of the Safe Speed road safety campaign Paul Smith 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 said it was demanding 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," said Smith. "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.
Discussion
OK Devil's advocate question
Very true, so how many would be willing to have a tachograph or similar installed?
[/devil's advocate]
Yes Yes I know the correct answer is that the method of enforcement should be fair, accurate, impartial but the current system with cameras is a long way from that imho. Varies according to device in use.
safespeed said:
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.
Very true, so how many would be willing to have a tachograph or similar installed?
[/devil's advocate]
Yes Yes I know the correct answer is that the method of enforcement should be fair, accurate, impartial but the current system with cameras is a long way from that imho. Varies according to device in use.
Excellent! Add to that the simultaneous Inside Out programme in the North East proving a traffic cop wrong about the 'speed kills' message and there was some excellent reportage from the Beeb last night.
Of course, this traffic cop (who 'enjoyed his job 'saving lives''), despite the overwhelming evidence of bad driving versus 'speed', refused to believe a word of it
Of course, this traffic cop (who 'enjoyed his job 'saving lives''), despite the overwhelming evidence of bad driving versus 'speed', refused to believe a word of it
echo said:
As a matter of interest how many brick walls have been prosecuted for speeding using laser evidence?
And how may drivers prosecuted for doing 4 mph when they were stationary?
I didn't see the program unfortunately so I may be missing something here...?
The point is the guns can give incorrect speed readings, and therefore should not be used for evidence.
Who do you work for?
Message poster on BBC Web page said:
Look at the web forums that have sprung up that are populated by alleged offenders desperately trying to obfuscate the legal process. Many of them have members very willing to aid those receiving tickets in getting away with offences they have admitted to on a public website. www.pepipoo.com www.pistonheads.com www.safespeed.org.uk there are many more.
Ted/Paul, I guess you have seen this comment amongst the postings immediatley following the BBC story?
Look at the web forums that have sprung up that are populated by alleged offenders desperately trying to obfuscate the legal process. Many of them have members very willing to aid those receiving tickets in getting away with offences they have admitted to on a public website. www.pepipoo.com www.pistonheads.com www.safespeed.org.uk there are many more.
Ted/Paul, I guess you have seen this comment amongst the postings immediatley following the BBC story?
deeen said:
The point is the guns can give incorrect speed readings, and therefore should not be used for evidence.
Who do you work for?
deeen getting a little paranoid?
Just saying that the errors reported above don't seem to relate to design use of the device.
It's like complaining that a car doesn't float very well - it's not designed to.
If you want something to measure the speed of walls or stationary cars accurately I suggest that a laser gun is not the best tool.
echo said:
If you want something to measure the speed of walls or stationary cars accurately I suggest that a laser gun is not the best tool.
Clearly not, but if you want to measure the speed of a moving vehicle then a device that cannot tell that a wall is not moving is not the best tool.
echo said:
If you want something to measure the speed of walls or stationary cars accurately I suggest that a laser gun is not the best tool.
That's as maybe, but are you saying that, knowing the inherent errors, you'd be totally happy being done for doing 33mph in a 30mph limit with one of these laserguns as the only evidence? What if you were sure you were under the limit? Hmmm...
Stace.
>> Edited by stace3610 on Tuesday 1st March 12:49
echo said:
Just saying that the errors reported above don't seem to relate to design use of the device.
It's like complaining that a car doesn't float very well - it's not designed to.
If you want something to measure the speed of walls or stationary cars accurately I suggest that a laser gun is not the best tool.
On the contrary...at least some of these errors are likely to be caused by the operation of the machine...e.g. moving the focal point while taking a reading.
As for the technical side - any device which measures speed is actually measuring change of distance over a known period of time. And all lasers do is measure distance - speed of laser is known to be c, therefore the using the time between pulse and return, a distance can be calculated. Using 2 or 3 pulses will then give you a good estimate of the speed of the target.
Therefore, as a brick wall is a FIXED distance away, the speed measured should always be 0. Unless there is either a technical problem, a design flaw, or user error. And if user error is that easy to do, with law-enforcement based on it, there is a serious procedural issue!
An absolute discrace, but stands to reason when you think about it really. If you are pointing a dot at the number plate of a fast moving object up to 400 meters away or more, unless you are Luke Skywalker you are absolutely bound to hit other areas apart from the number plate and ever other vehicles......
Reasonable doubt in a lot of cases I would say?
Cheers,
Steve
Reasonable doubt in a lot of cases I would say?
Cheers,
Steve
As far as walls and stationary cars are concerned these are red herrings. The guns are NOT designed to do this and so do not have a design flaw - just a design limitation. They are designed with the understanding that they will NOT be used to measure the speed of very close stationary objects.
They are designed to detect small amounts of light reflected off an object hundreds of metres away.
Then again neither will they make a cup of tea
I'm more convinced by the sort of thing that fat audi 80 seems to be alluding to (ie inaccurate targeting) but I missed the programme so can't comment.
Just one other minor technical point..
"As for the technical side - any device which measures speed is actually measuring change of distance over a known period of time"
Not quite - there are many ways to measure speed (velocity) without reference to distance - including Doppler shift (radar) and by integrating force/acceleration and time.
sorry to bore...
They are designed to detect small amounts of light reflected off an object hundreds of metres away.
Then again neither will they make a cup of tea
I'm more convinced by the sort of thing that fat audi 80 seems to be alluding to (ie inaccurate targeting) but I missed the programme so can't comment.
Just one other minor technical point..
"As for the technical side - any device which measures speed is actually measuring change of distance over a known period of time"
Not quite - there are many ways to measure speed (velocity) without reference to distance - including Doppler shift (radar) and by integrating force/acceleration and time.
sorry to bore...
It seems odd that the designers didnt account for nearby objects.
When I did my final year project (a few year back now) I had to make a range finding device similar to that now used so speed measurment except I used sound where as they use light.
I had to have a tricky bit of circuitry to allow the return signal to not blow the amp that was using the same transmitter to recieve as obviusly at close range it would be louder, after a small amount of time if signal not heard then amp kicks in to listen to the fainter return.
And I thought that this type of device back then had limitations, being its fine for measuring distance but suffers far to much in errors for a uni project to measure speed. But I suppose commercial intrests are different, get it out, defend what you have, say its fine must be you, etc etc, see it every day in software eventually people say ohh your right it was crap but hear is the new and improved version
When I did my final year project (a few year back now) I had to make a range finding device similar to that now used so speed measurment except I used sound where as they use light.
I had to have a tricky bit of circuitry to allow the return signal to not blow the amp that was using the same transmitter to recieve as obviusly at close range it would be louder, after a small amount of time if signal not heard then amp kicks in to listen to the fainter return.
And I thought that this type of device back then had limitations, being its fine for measuring distance but suffers far to much in errors for a uni project to measure speed. But I suppose commercial intrests are different, get it out, defend what you have, say its fine must be you, etc etc, see it every day in software eventually people say ohh your right it was crap but hear is the new and improved version
echo said:
As far as walls and stationary cars are concerned these are red herrings. The guns are NOT designed to do this and so do not have a design flaw - just a design limitation. They are designed with the understanding that they will NOT be used to measure the speed of very close stationary objects.
They are designed to detect small amounts of light reflected off an object hundreds of metres away.
Then again neither will they make a cup of tea
I'm more convinced by the sort of thing that fat audi 80 seems to be alluding to (ie inaccurate targeting) but I missed the programme so can't comment.
Just one other minor technical point..
"As for the technical side - any device which measures speed is actually measuring change of distance over a known period of time"
Not quite - there are many ways to measure speed (velocity) without reference to distance - including Doppler shift (radar) and by integrating force/acceleration and time.
sorry to bore...
For what it's worth laser speed guns use sequential range-findings to determine speed. I find it a little hard to imagine how such a device could be designed so that it would get confused when range-finding on a stationary object. Stationary or moving, the device is measuring the time taken for a reflection to be picked up. The reflection is not that hard to discriminate from background light as it is monochromatic, fairly well polarised and has a distinctive signature (i.e. a very sharp rising edge and a known pulse width). At the very least, if the detector is saturated or the range-findings are not closely clustered around one distance, the device should easily be able to recognise that it isn't working properly. It should be almost impossible for it to come up with a spurious readings.
Hi all,
At first it might seem that obtaining a speed reading from a wall is not relevant. Here is why it is.
The laser beam is invisible.
The devices are therefore equipped with a targeting mechanism which as part of the set up, must be aligned with the invisible laser beam.
Say this part of the setup is neglected or not done properly.
If the operator follows a car with the sighting mechanism, but the laser is not aligned with the sighting mechanism he might actually be following something else with the laser without knowing it. Like a wall.
Since the devices are quite capable of obtaining readings when they are panned along a wall, how do you now prove whether the speed reading was obtained from tracking the car or the wall?
You can't. Because the laser is invisible.
The programme contained an interview with Mr. Garratt where he indicated that operators do not always follow the correct prodedures.
Hope this helps.
At first it might seem that obtaining a speed reading from a wall is not relevant. Here is why it is.
The laser beam is invisible.
The devices are therefore equipped with a targeting mechanism which as part of the set up, must be aligned with the invisible laser beam.
Say this part of the setup is neglected or not done properly.
If the operator follows a car with the sighting mechanism, but the laser is not aligned with the sighting mechanism he might actually be following something else with the laser without knowing it. Like a wall.
Since the devices are quite capable of obtaining readings when they are panned along a wall, how do you now prove whether the speed reading was obtained from tracking the car or the wall?
You can't. Because the laser is invisible.
The programme contained an interview with Mr. Garratt where he indicated that operators do not always follow the correct prodedures.
Hope this helps.
echo said:
As far as walls and stationary cars are concerned these are red herrings. The guns are NOT designed to do this and so do not have a design flaw - just a design limitation. They are designed with the understanding that they will NOT be used to measure the speed of very close stationary objects.
Let's be quite clear about what they are designed to do. The Lti 2020 sends out 43 pulses of IR light in 1/3rd second. The distance of a reflective object is measured 43 times by the flight time of each light pulse. The 43 flight times are assembled into a 'ramp' and up to five of them may be discarded if they don't fit the ramp. If the ramp accuracy (i.e. self similarity) isn't better than about 2mph then the device displays 'error'. Otherwise it displays a speed based on the slope of the ramp. (The numbers in this section are from memory)
Unfortunately it knows absolutely nothing about movement - it only knows about ramps. It does not and cannot know anything about the path of the light, nor anything about the reflective object or objects.
Sweeping the measurement beam across a wall or a road surface produces a ramp and that ramp might be interprited as a speed reading.
It's quite possible to get a speed reading while panning the beam in an attempt to acquire or track a car. How often does this happen in practice? We don't have any idea. I'd be damn surprised if it was less frequent than 1 in 100, and that should be game over for the dodgyscope.
Everyone needs to ask exactly why the CPS are so damn reluctant to disclose LTI2020 traffic videos. See:
www.safespeed.org.uk/pr111.html
>> Edited by safespeed on Wednesday 2nd March 02:34
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