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Police Radar Accuracy?


AJRFulton

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I got caught speeding today in the Z, during a long distance drive, doing 89mph somewhere just south of Lockerbie. I was, surprisingly let off with a wrap on the knuckles after arguing my case until I was blue in the face.

 

I drive 30,000mls a year. I'm reasonably savvy to motorway driving and it's kept me with a clean licence for the 10yrs I've been a high milage driver. This journey was no different, I did the same thing I always do - set the cruise control to 77mph using the GPS, and leave it on. The cruise control was active as I drove past the radar, and the GPS read 77mph, naturally as you drive past a radar trap, you always do check your speed. I've every faith that my GPS is very accurate when calculating speed over a distance, and I would of been doing that speed constantly for at least the previous 25mls.

 

Now 77mph roughly translates to 82mph on the cruise setting/clock, and the engine is almost exactly on 3000rpm in 6th (some boffin can work out if that checks out).

 

Now whilst I've got away with it today, it got me questioning how many other poor sods haven't? How accurate are are these radars? Does the Z's aluminium panels and angles make it unreliable? I don't know.

 

The one that caught me, I forget the model, had sort of binocular type lenses, and another lens on the side (I'd assume this was for looking through). There was a LCD display on one side displaying the time/date/speed. Whilst the radar looked fairly new, I would say it was designed in the 90's.

 

If they went ahead and fined me, could I even do anything about it? Have I been lucky to argue my case?

 

Edit the gun used looked the same as the one in this BBC article.

Edited by AJRFulton
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I read once that with the laser operated it must read off the front of the car and a flat not angled part of the car. I couldn't quite get that because all cars are angulated or inconsistently shaped through design.

 

How true this is I do t know. But knowing the "law" I guess they can get out of any excuse to nab you.

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I was on the outside lane, the police were about 10m in from the motorway side on one of those little runways they have. They got a speed lock at 100m exactly (nice and easy to remember for me). They were at a fair angle to me. Assuming around 20-25m in from my car, and with a 100m diagonal to my car.

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so they said you were doing 89mph

your speedo said 82 and

sat nag said 77

 

is that correct

 

if thats the case then, I suspect the callibration of their machine was way off - as it should read your "actual" ground speed ie 77 (or thereabouts)

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As far as I know you're within your rights to ask to see the calibration certificate for that particular piece of equipment so that you can check the calibration dates (but don't quote me on that)

correct - at the very least Freedom of information act kicks in

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As far as I know you're within your rights to ask to see the calibration certificate for that particular piece of equipment so that you can check the calibration dates (but don't quote me on that)

correct - at the very least Freedom of information act kicks in

 

That's right it has to be calibrated on a regular basis. Forgot about that.

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As far as I know you're within your rights to ask to see the calibration certificate for that particular piece of equipment so that you can check the calibration dates (but don't quote me on that)

 

They've not ticketed me, so no need to take it that far.

 

The officer assured me everything was in date and daily checks/calibration checks had been carried out.

 

I'm thinking from researching the types of speed gun, this wasn't a radar, but a handheld laser speed gun.

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I think its roughly 28 m.p.h per 1,000 revs in 6th, so 84 m.p.h.

 

 

Pete

 

That's above both what my speedo and GPS read. The needle just above the 80mph, and 77mph on the GPS is pretty much spot on 3k revs. Of course the rev meter may be ever so slightly out, as I doubt that is scrutinised for serious accuracy.

 

I trust my GPS for greatest accuracy over long distance.

Edited by AJRFulton
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I think they have to point the laser at a flat surface ie your number plate , that's why motorbike tickets could be argued as no plate or flat surface on the front.

That's how I've always understood it but I may be wrong!

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But isn't the speed limit 70 in Scotland as well or am I missing something..

 

are you allowed to drive faster than us Southern's :scare: :scare:

 

Yip, I couldn't argue if I got done for going 77mph on the motorway. However I'd consider myself unlucky if that ever did happen.

 

However it's a calculated risk, that shortens my journey by about an hour in flowing traffic, and to this point I've never been pulled over for doing 77mph on a motorway.

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But isn't the speed limit 70 in Scotland as well or am I missing something..

 

are you allowed to drive faster than us Southern's :scare: :scare:

 

Yip, I couldn't argue if I got done for going 77mph on the motorway. However I'd consider myself unlucky if that ever did happen.

 

However it's a calculated risk, that shortens my journey by about an hour in flowing traffic, and to this point I've never been pulled over for doing 77mph on a motorway.

 

Your lucky as my mate got done on the M1 by a chopper for doing 75 MPH,

 

not sure the 77 MPH is a valid excuse down here.

 

Sure all on here will tell me different, which is good as I'll now up my cruise to 80 MPH. :yahoo:

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