For BIB re: speeding - Has anyone heard of this?
Discussion
Interesting scenario... would really appreciate any and all comments and opinions:-
two cars travelling on motorway. Car 1 in lane 1 and Car 2 in lane 2. Car 1 is slightly ahead and accelerating away from Car 2 (not by much).
Police laser both cars to check speed. Car 1 is within the speed limit. Car 2 is recorded at 102 mph.
Police fire down motorway ramp and catch Car 2. Car 2 pulls over (speed when stopped 63mph).
Police officer shows Car 2 driver the 102 laser reading. Car 2 driver says there has been an error and asks police officer to sign a statement as to the proximity and speed of Car 1.
Police officer agrees and signs the following statement:-
Car 1 and Car 2 travelling together on motorway. Car 1's speed was under 70 mph and Car 2's speed was 102.
Car 2 Driver also has a record of the onboard computers trip readings showing an average speed for the journey at 44 mph (route in gps details roads as either duel carriageways and motorway)
Questions...
Has anyone ever heard of a police officer signing a statement at the side of the road before?
Is it possible for a laser gun used by English police forces to deliver a false reading?
Does Car 2 driver have any sort of case given he is in possession of the police officers statement and onboard computer records?
Regards,
N
trinitycall said:
Has anyone ever heard of a police officer signing a statement at the side of the road before?
Is it possible for a laser gun used by English police forces to deliver a false reading?
Does Car 2 driver have any sort of case given he is in possession of the police officers statement and onboard computer records?
Regards,
N
The police officer is simply signing what he's going to write in his statement when he prosecutes the 102mph driver...
The fact there was another car present...isn't a problem with a laser gun. With a radar gun, it might be.
As for false readings; anything is possible in life.
As for your trip computer....not worth zilch....The trip computer on the Volvo often records my average speed at 33mph, when I've spent the last few hours on the motorway...at excess that speed..
What's this hang up about the police officers' statement.??????????????
The cop has said that car 2 was in excess of car 1's speed. Nothing wrong with that...
Streetcop said:
The police officer is simply signing what he's going to write in his statement when he prosecutes the 102mph driver...
The fact there was another car present...isn't a problem with a laser gun. With a radar gun, it might be.
As for false readings; anything is possible in life.
As for your trip computer....not worth zilch....The trip computer on the Volvo often records my average speed at 33mph, when I've spent the last few hours on the motorway...at excess that speed..
What's this hang up about the police officers' statement.??????????????
The cop has said that car 2 was in excess of car 1's speed. Nothing wrong with that...
Thanx for the info... just by way of clarification. The statement was drafted by Car 2 driver to say that Car 1 and Car 2 were travelling together along the motorway. The police officer acknowledged this and even provided details as to Car 1 to Car 2 driver.
The question arises - how is it possible for Car 2 to be travelling beside Car 1 when supposedly doing an extra 30mph?
is it usual for police officers to sign a statement drafted by a car driver at the road side to back up the drivers claim that the laser reading was inaccurate?
I've certainly never heard of this.
Regards,
N
Laser guns can give "sweep eerrors". In other words, if the "focus patch" of the gun moved from one point to another while the reading was being taken, the speed given would be wrong.
If the car was moving away from the gun, for example, and the focus patch started on the rear number plate but finished on any point further forward on the car (wing mirror, rear window etc.) the car would appear to be going faster than it really was.
You can prove this by doing it on a stationary car and seeing how fast the gun makes it go!
If the car was moving away from the gun, for example, and the focus patch started on the rear number plate but finished on any point further forward on the car (wing mirror, rear window etc.) the car would appear to be going faster than it really was.
You can prove this by doing it on a stationary car and seeing how fast the gun makes it go!
trinitycall said:
The question arises - how is it possible for Car 2 to be travelling beside Car 1 when supposedly doing an extra 30mph?
is it usual for police officers to sign a statement drafted by a car driver at the road side to back up the drivers claim that the laser reading was inaccurate?
I've certainly never heard of this.
Regards,
N
It's got to be along side another car to overtake it...but obviously the quicker the speed difference, the less time both cars spend alongside..
As for signing. Up to the copper in question. He has nothing to hide. He's not telling lies. There was another car on the road and that car was car 1 and was 30mph slower than car 2.
The cop will write that on his own statement, so was being polite and tolerant by signing that on the paper that car 2 driver had.
I suppose the cop will be thinking..."i'll sign all I want mate...as it'll be as much use as a chocolate fireguard defending you on this offence"...
deeen said:
Laser guns can give "sweep eerrors". In other words, if the "focus patch" of the gun moved from one point to another while the reading was being taken, the speed given would be wrong.
If the car was moving away from the gun, for example, and the focus patch started on the rear number plate but finished on any point further forward on the car (wing mirror, rear window etc.) the car would appear to be going faster than it really was.
You can prove this by doing it on a stationary car and seeing how fast the gun makes it go!
The 'focus patch' you describe would have to move backwards and forwards between these two points several times as the gun uses more than 1 pair of readings and rejects those that are not consistent.
The stationary car thing is a seperate issue with zero readings.
>> Edited by echo on Monday 28th February 11:22
deeen said:
Laser guns can give "sweep eerrors". In other words, if the "focus patch" of the gun moved from one point to another while the reading was being taken, the speed given would be wrong.
If the car was moving away from the gun, for example, and the focus patch started on the rear number plate but finished on any point further forward on the car (wing mirror, rear window etc.) the car would appear to be going faster than it really was.
You can prove this by doing it on a stationary car and seeing how fast the gun makes it go!
Interesting... If you are lasered can you ask for video evidence that the laser was not moving around when pointed at you?
Streetcop said:
The cop will write that on his own statement, so was being polite and tolerant by signing that on the paper that car 2 driver had.
I suppose the cop will be thinking..."i'll sign all I want mate...as it'll be as much use as a chocolate fireguard defending you on this offence"...
Thought as much. I guess the only worrying factor here is that Car 1 and Car 2 had been just about side-by-side for over a mile
Thanx,
N
deeen said:
Laser guns can give "sweep eerrors". In other words, if the "focus patch" of the gun moved from one point to another while the reading was being taken, the speed given would be wrong.
If the car was moving away from the gun, for example, and the focus patch started on the rear number plate but finished on any point further forward on the car (wing mirror, rear window etc.) the car would appear to be going faster than it really was.
You can prove this by doing it on a stationary car and seeing how fast the gun makes it go!
Sounds very plausible...
In reality doesn't work...
I've tried it...often..
Shop windows, white lines, street signs etc...result 0mph
Point it at a moving car, for example, 40mph...then driver sees me...press trigger again, 37mph, then trigger again 25mph as the car crawls past me...
trinitycall said:
two cars travelling on motorway. Car 1 in lane 1 and Car 2 in lane 2. Car 1 is slightly ahead and accelerating away from Car 2 (not by much).
Police laser both cars to check speed. Car 1 is within the speed limit. Car 2 is recorded at 102 mph.
Can I suggest that the question is re-read, It's interesting to note the presumption of guilt from some quarters, check the facts, car 1, the slower according to the police was accelerating away from car 2, the car they stopped for speeding having stated that car 1 was within the speed limit. Two possible conclusions, Speed trap malfunction, traffic cop stupidity.
Would also call into question the policeman's 'prior estimate of excessive speed'.
This may make an interesting day in court, would need to have the policeman there as a witness to explain how car 2 could be dropping back from car 1 whilst car 1 is only doing 70mph, yet car 2 is doing 102 mph?
This may make an interesting day in court, would need to have the policeman there as a witness to explain how car 2 could be dropping back from car 1 whilst car 1 is only doing 70mph, yet car 2 is doing 102 mph?
kevinday said:
Would also call into question the policeman's 'prior estimate of excessive speed'.
This may make an interesting day in court, would need to have the policeman there as a witness to explain how car 2 could be dropping back from car 1 whilst car 1 is only doing 70mph, yet car 2 is doing 102 mph?
Quite,
as I said, bad equipment at best, jobsworth with low brain cell count dosn't help
echo said:
The 'focus patch' you describe would have to move backwards and forwards between these two points several times as the gun uses more than 1 pair of readings and rejects those that are not consistent.
The stationary car thing is a seperate issue with zero readings.
>> Edited by echo on Monday 28th February 11:22
I disagree, the way it was explained to me if you moved it backwards and forwards it would give an error reading instead of a speed as the readings would be inconsistent. However, the gun is blind - it does not know what it is looking at. So a single sweep (such as when trying to track a moving car, for example) gives a false speed (which i confusingly called a sweep error) because the gun can't tell the difference between the point of reflection moving along the car, and the point of reflection being fixed and the car moving. The operator just sees a speed, and has no indication it is wrong (unless the target is being overtaken by a "slower" car, as per this post!).
Stationary car thing - why should this be seperate? Sounds suspiciously like propaganda from the ppl who would like us to believe that laser gun evidence is infallible. I don't think the gun realises the car is stationary and thinks "ooh, that car's not moving, I'd better give a false reading now, but I promise I'll never do it again"! Of course, if you can explain the physics behind your statements, it would be very interesting to read it.
Street - roadsign flat, no chance of sweep error. White lines - surprised you get a reading at all (unless you're firing downwards). Buildings - keep trying! I have an eyewitness account of one false reading in five.
>> Edited by deeen 'cos i think my "error" and echo's "error" are at cross porpoises.
>> Edited by deeen on Monday 28th February 11:58
In order to give a reading the gun will need several readings together which show a very similar ratio to each other. These readings happen VERY quickly.
Most parts of the car are travelling at the same speed so in your example you would get a bunch of readings from the first part of the car then a bunch from the second. There may be a few in between that show a faster 'speed' due to the movement but these would be rejected.
Just my opinion - and not any propaganda
echo said:
In order to give a reading the gun will need several readings together which show a very similar ratio to each other. These readings happen VERY quickly.
Most parts of the car are travelling at the same speed so in your example you would get a bunch of readings from the first part of the car then a bunch from the second. There may be a few in between that show a faster 'speed' due to the movement but these would be rejected.
Just my opinion - and not any propaganda
Ok this is how it was explained to me.
The gun can't get a speed from a single reading because the speed of light is constant. The readings are only measuring distance. The gun has to take at least two distance readings and measure the difference between them. The parts of the car are all moving at the same speed, but this is a red herring beacause each individual reading is not speed, it is only distance. If the first and second reading are both off the number plate, the gun knows how far the car has moved (the difference in distance) and the time between the readings and can work out the speed. If the first reading is off the number plate and the second off the wing mirror, the gun has a diffrernce in distance and the time between readings and works out a false speed, because the difference in distance is not purely down to the movement of the car. The gun has no way of knowing if its readings are different because of the speed the car is moving, or because the readings are from two different points on the car, or a combination of the two.
The model of gun that was explained to me takes 30 readings (yes in very short space of time) and discards the least consistent 10 readings. If the remaining 20 appear consistent (according to the gun's internal program) the gun will give a reading. If not, it will give an error message. If the gun is foccused on the same point over these 20 readings, the speed will be correct. If not, the speed will be wrong. There is no way of knowing.
I've just re-read this, not v. clear perhaps but can't think how to explain it properly! I know what I mean!
Of course, with a couple of pint glasses to hand, all would become clear...
>> Edited by deeen to add more detail on Monday 28th February 12:55
>> Edited by deeen on Monday 28th February 13:19
hedders said:
Interesting... If you are lasered can you ask for video evidence that the laser was not moving around when pointed at you?
A good question. Digital imagers are sensitive to Infra-Red (IR), which is what the laser gun is emitting. However, IR filters are usually coated onto the optics of the camera; hence the reflected IR will be blocked before it reaches the imager. Therefore the targeted area cannot be identified.
deeen said:
The model of gun that was explained to me takes 30 readings (yes in very short space of time) and discards the least consistent 10 readings. If the remaining 20 appear consistent (according to the gun's internal program) the gun will give a reading. If not, it will give an error message. If the gun is foccused on the same point over these 20 readings, the speed will be correct. If not, the speed will be wrong. There is no way of knowing.
Not quite...
It discards anything that does not show a consistant sequence of readings - If the device measures any jump in speed readings (ie a step-change in the 'rate of change' of distance) it will reject the whole bunch.
echo said:Highlight added for emphasis
Not quite...
It discards anything that does not show a consistant sequence of readings - If the device measures any jump in speed readings (ie a step-change in the 'rate of change' of distance) it will reject the whole bunch.
What if the beam was swept along the side of a car? Would a sweep along this nice flat-ish surface result with an error?
What if the operator was enforcing a straight road and completely missed the target car such that he swept the tarmac instead? With the distances and angles involved, surely this would produce a non-zero velocity?
supraman2954 said:
What if the beam was swept along the side of a car? Would a sweep along this nice flat-ish surface result with an error?
What if the operator was enforcing a straight road and completely missed the target car such that he swept the tarmac instead? With the distances and angles involved, surely this would produce a non-zero velocity?
You need a decent reflection to be detected - I'm not convinced that the side of a vehicle or the road surface would give anywhere like enough reflection at the sort of obtuse angle youd get from behind or in front of a vehicle at several hundred meters.
Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff