VASCAR -minumum distance measured
Discussion
got "invited" to court for doing 107.6 mph at around 11 pm on the M62 sometime in December last year. Copper pulled out of a petrol station right behind me when i was following 2 other cars, junction before I was coming off anyway.
In the last corner I overtook the two cars I was following on the outside and got pulled over right after.
Thing is that the only had the thing
on me for 0.248 of a mile, which seems a little short, so I'm hoping that's something I can work with.
Is there a minimum distance one's gotta be followed for before it's legally binding?
In the last corner I overtook the two cars I was following on the outside and got pulled over right after.
Thing is that the only had the thing
on me for 0.248 of a mile, which seems a little short, so I'm hoping that's something I can work with.
Is there a minimum distance one's gotta be followed for before it's legally binding?
The Police vehicle is fitted with a system that converts the revolutions of the car prop shaft into distance via magnets strapped to the prop shaft. The revolutions are counted by a sensor bolted to the car body. This is transfered to the VASCAR head in the vehicle cockpit. The distances used on pre-fed checks are vary accurate because the operator will (where possible) stop at the first point to be used and activate the distance switch. The Police vehicle is then driven to the next static point with the distance being recorded until it is stopped over or under or next to the second point to be used. The distance must exceed 2/10ths of a mile.
this from madcop in the VASCAR - HELP?? post.
I'm guessing that means i'm screwed?
madcop on the other thread rightly points out that the error is greatest on the smallest distances.
Considering the errors, if the distance is measured right, at 107 you will take 8.34 sec to traverse the run bewteen the timing points. There will be a very small error between the police opeartor observing you and throwing the switch and the timing starting or stopping. Reaction time is quoted at variously 150 millisec and 300millisec from the adrenaline high jet fighter pilot to the more average human being.
In most cases timing delay will be about the same plus/minuis 100 millisec. But it might be possible to argue that an experimental measurement is subject to subconscious skewing of reaction as the nature of observing a car suddenly at the start of a run and at the end where the event can be observed with a greater degree of expectation.
In this case experimental procedure could require the full 300 millisec error band to be applied to both readings. i.e. the police operator could have thrown the time switch 0.3 seconds late at the start of the run and 0.3 early at the end.
Inferring that the time interval that gave 107 point whatever was 8.34 sec, increasing this time to 8.93 gives 146.46 sec which is just about 99.5 mile/h.
Of course theres a similar argument that applying the same error band means you could have been averaging 114 or so.
I assume that the Vascar cars are calibrated at 60 so the effect of tyre expansion is nulled out over an acceleration from slow to 100 plus. If the calibration is at 20 then your speed might be overestimated by another 0.6 - 1 mile/h.
I can't comment on parallax errors - they are dependant on the points selected but I'd assume he was closer to you at the start of the run than at the end unless he was driving something really serious.
Since theres more severe consequences for having it proved that you were over the ton then you might decide to go for this argument while accepting that you were guilty at least of exceeding the limit.
And this sort of thing shows the false nature of measurements described to 2 places of decimals when the actual result could be plus minus 7-10 mile/h.
Just like a digital watch - you read it to the second whe it might be minutes out
Considering the errors, if the distance is measured right, at 107 you will take 8.34 sec to traverse the run bewteen the timing points. There will be a very small error between the police opeartor observing you and throwing the switch and the timing starting or stopping. Reaction time is quoted at variously 150 millisec and 300millisec from the adrenaline high jet fighter pilot to the more average human being.
In most cases timing delay will be about the same plus/minuis 100 millisec. But it might be possible to argue that an experimental measurement is subject to subconscious skewing of reaction as the nature of observing a car suddenly at the start of a run and at the end where the event can be observed with a greater degree of expectation.
In this case experimental procedure could require the full 300 millisec error band to be applied to both readings. i.e. the police operator could have thrown the time switch 0.3 seconds late at the start of the run and 0.3 early at the end.
Inferring that the time interval that gave 107 point whatever was 8.34 sec, increasing this time to 8.93 gives 146.46 sec which is just about 99.5 mile/h.
Of course theres a similar argument that applying the same error band means you could have been averaging 114 or so.
I assume that the Vascar cars are calibrated at 60 so the effect of tyre expansion is nulled out over an acceleration from slow to 100 plus. If the calibration is at 20 then your speed might be overestimated by another 0.6 - 1 mile/h.
I can't comment on parallax errors - they are dependant on the points selected but I'd assume he was closer to you at the start of the run than at the end unless he was driving something really serious.
Since theres more severe consequences for having it proved that you were over the ton then you might decide to go for this argument while accepting that you were guilty at least of exceeding the limit.
And this sort of thing shows the false nature of measurements described to 2 places of decimals when the actual result could be plus minus 7-10 mile/h.
Just like a digital watch - you read it to the second whe it might be minutes out
Richard C said:I assume that the Vascar cars are calibrated at 60 so the effect of tyre expansion is nulled out over an acceleration from slow to 100 plus. If the calibration is at 20 then your speed might be overestimated by another 0.6 - 1 mile/h.
VASCAR is not calibrated at all by the use of speed. It is calibrated over a measured mile.
The car is stopped at the start of the measured mile so the centre of the car (door pillar between front and rear doors) is level with the marker. It is then driven to the measured end mile marker and stopped next to the marker post in the same method as before. It does not matter how fast this distance is travelled.
At the commencement of the calibration check, the distance switch is activated. at the conclusion it is de-activated. The measured mile is then stored into the VASCAR head. A short time (two or three seconds will sufice) is then activated into the VASCAR head via the time switch which, when the device is set in calibration mode (as it would be for this procedure)gives a clibration number which is then entered into the machine. This having been completed calibrates the machine to exactly 1 mile. The clock has a self check on it. The device is then ready for use.
There is no speed involved at all in the calibration of VASCAR other than that involved to propel the car from the first calibration point until it reaches the second one. Distance is the critical measurement in this procedure and not speed in any way.
It does not matter how fast this distance is travelled.
There I have to disagree with you. I agree that the Vascar is calibrated by using a DISTANCE not a speed. But the only why that distance is measured is independent of the speed that it is traversed is if the Vascar cra had solid wheels and tyres. Which it has not. Pneumatic tyres have a rolling radius. That rolling radius changes and increases with speed. The pulse sensor on the propshaft will give a distance per pulse. That distance will be only be accurate at a given speed. If the distance that is later measured for a trap is traversed at the same speed or a prusuit is carried out at the same speed that is OK. But if the speed is highre, the tyre rolling radius increses and the distance measured is less than the real disatnce. And any speed measured using that distance will be higher. Maybe by a samll amount but 1 /2 to 1 and a half percent is not inconsiderable.
Richard C said:
Maybe by a samll amount but 1 /2 to 1 and a half percent is not inconsiderable.
err.so 101 mph or 100.5 mph is not an inconsiderable difference against an actual speed of 100 mph..!? methinks that would be nullified (or amplified) by the reactions of the person starting and stopping the timing run... either way.. you're never going to get away with that one as a line of argument
Matt.
Richard C said:
There I have to disagree with you. I agree that the Vascar is calibrated by using a DISTANCE not a speed. But the only why that distance is measured is independent of the speed that it is traversed is if the Vascar cra had solid wheels and tyres. Which it has not. Pneumatic tyres have a rolling radius. That rolling radius changes and increases with speed. The pulse sensor on the propshaft will give a distance per pulse. That distance will be only be accurate at a given speed. If the distance that is later measured for a trap is traversed at the same speed or a prusuit is carried out at the same speed that is OK. But if the speed is highre, the tyre rolling radius increses and the distance measured is less than the real disatnce. And any speed measured using that distance will be higher. Maybe by a samll amount but 1 /2 to 1 and a half percent is not inconsiderable.
And I would submit that this calculation is so minute as to not be worth worrying about.
You are talking about fractions of an inch in increasing wheel diameters from hot and cold tyres and in anycase the tyres do not suddenly become larger because you run the distance over a measured mile at 60mph as oppose to 20mph if they are already hot from chasing someone at 130mph all morning.
This arguement is quite frankly useless.
{quote]err. so 101 mph or 100.5 mph is not an inconsiderable difference against an actual speed of 100 mph..!? methinks that would be nullified (or amplified) by the reactions of the person starting and stopping the timing run... either way.. you're never going to get away with that one as a line of argument
Maybe 1.5% is minute. And this is the range of error that diferent speeds and temperatures create. In the eyes of the bench, thanks to a Lord Chancellors dept fixated on such minute differences, the difference between 99 and 100.5 can be a ban or not. The argument did work for me.
Maybe 1.5% is minute. And this is the range of error that diferent speeds and temperatures create. In the eyes of the bench, thanks to a Lord Chancellors dept fixated on such minute differences, the difference between 99 and 100.5 can be a ban or not. The argument did work for me.
I was nicked f6r 100.020 in Exeter mid 90's. Only car on the road etc. Bench had reputation for banning. Obtrained manufacturers data sheet data sheet for Megitt instrument that bthey used which clearly states accuracy is +/- 2 mile/h or +/- 2% whichever is greater. ( for reasons given earlier in this thread ) Argued that it would be unreasonable to ban me as it could not be certainly proved I was doing >100. Bench didn't like it and hit me with 5 oints and £ 260 fine.
Police didn't like it and tried to argue that they were trained to use it to better than 0.1 mile/h which is false for reasons given earlier. Also that it was totally accurate as it had been calibrated etc....
I don't think really the bench, the police or the solicitor I hired understood the issues but in the end the data sheet did it as it was the only evidence offered as to accuracy of vascar.
Police didn't like it and tried to argue that they were trained to use it to better than 0.1 mile/h which is false for reasons given earlier. Also that it was totally accurate as it had been calibrated etc....
I don't think really the bench, the police or the solicitor I hired understood the issues but in the end the data sheet did it as it was the only evidence offered as to accuracy of vascar.
Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff