Hi all,
Just coming back to yard after work and I face police speed gun on 40mph zone. I’m sure I was doing 45 when they spotted me, facing gun at my lorry for 5-10 seconds. but I put my brakes on and within few seconds I was under the speed limit. Can’t figure out weather I got caught or not…
If they put gun towards ur number plate which speed does they count ?
IIRC speed guns operate by sending out radar waves and measuring the “Doppler shift” (that is the difference of the returning frequency to the transmitted one) to determine the speed of the measure vehicle. However, since the measured vehicle is usually moving at a tangent to the measuring device ( you never see a copper stood in the middle of the road!) there is an inherent inaccuracy that must be corrected.
Hope that helps.
Does their guns are set with “wiggle room” of 10% like most speed cameras ?
Was your number plate going slower than the truck??
They allow a certain percentage over the limit,and with speedo`s not being entirely accurate you may have been within the speed tolerance
Captain Caveman 76:
IIRC speed guns operate by sending out radar waves and measuring the “Doppler shift” (that is the difference of the returning frequency to the transmitted one) to determine the speed of the measure vehicle. However, since the measured vehicle is usually moving at a tangent to the measuring device ( you never see a copper stood in the middle of the road!) there is an inherent inaccuracy that must be corrected.
You going for a different physics lesson each day of this week mate? 
If you see em it’s usually too late, just be a bit nervous for the next few weeks and see what happens.
Usually I add on 10% for the speed quoted on tinterweb so for 50 you might get a speed awareness course option.
I got a 36 in a 30 last month. Stupid mistake on my part.
Been offered the course which I’m attending on Monday next week.
Generally it’s 10%+ 2mph as the threshold, but not all forces follow that. It takes less than a second for them to get your speed, so if you’ve seen them, braking is pointless as it’s too late.
Captain Caveman 76:
IIRC speed guns operate by sending out radar waves and measuring the “Doppler shift” (that is the difference of the returning frequency to the transmitted one) to determine the speed of the measure vehicle. However, since the measured vehicle is usually moving at a tangent to the measuring device ( you never see a copper stood in the middle of the road!) there is an inherent inaccuracy that must be corrected.Hope that helps.
There’s no need to correct for this as it will always work in the favour of the driver - i.e. The speed recorded by the radar due to this will always be less than or equal to the vehicle’s actual speed on the road.
Dipper_Dave:
If you see em it’s usually too late, just be a bit nervous for the next few weeks and see what happens.Usually I add on 10% for the speed quoted on tinterweb so for 50 you might get a speed awareness course option.
I’m for sure not 50, could be 45 max.
Fingers crossed, anxious wait for the postman for few days… 
Captain Caveman 76:
IIRC speed guns operate by sending out radar waves and measuring the “Doppler shift” (that is the difference of the returning frequency to the transmitted one) to determine the speed of the measure vehicle. However, since the measured vehicle is usually moving at a tangent to the measuring device ( you never see a copper stood in the middle of the road!) there is an inherent inaccuracy that must be corrected.Hope that helps.
Won’t be driving Lorries if I can understand this 
Neil20:
Captain Caveman 76:
IIRC speed guns operate by sending out radar waves and measuring the “Doppler shift” (that is the difference of the returning frequency to the transmitted one) to determine the speed of the measure vehicle. However, since the measured vehicle is usually moving at a tangent to the measuring device ( you never see a copper stood in the middle of the road!) there is an inherent inaccuracy that must be corrected.Hope that helps.
Won’t be driving Lorries if I can understand this
It’s not complex if explained by a good teacher, hence Cavey is now driving a truck! 
Get some C.D. discs on the window. Mount then so they move with the vehicle movement. Has worked several times for me.
If you haven’t been caught speeding in the previous 3 years…
You’ll get an offer of a speed awareness course. If you were doing 45 in a 40, you’ll be getting a ticket.
The margin is 6% not 10% +2 mph.
I agree with you, it ■■■■■
ringfur:
Get some C.D. discs on the window. Mount then so they move with the vehicle movement. Has worked several times for me.
Like all good traffic cops will deliberately aim the radar at a CD stuck in yer windscreen? Never heard so much tosh in all my days.
yourhavingalarf:
Never heard so much tosh in all my days.
Have you not been reading CF’s posts then? 
yourhavingalarf:
If you haven’t been caught speeding in the previous 3 years…You’ll get an offer of a speed awareness course. If you were doing 45 in a 40, you’ll be getting a ticket.
The margin is 6% not 10% +2 mph.
I agree with you, it ■■■■■
Nope, ACPO guidelines are still 10% + 2mph. However, you can still get done for speeding at anything above the limit. Most speedometers read high these days. This is to account for tyre wear etc. So if you’re showing 45 then you’re more than likely only doing 43 / 44 in a truck. Cars are more inaccurate.
The radar style speed gun has been obsolete for a good few years now. They were never that accurate and could often pick up other vehicle behind you or travelling in the opposite direction.
These days most forces use pro-laser 3 guns. They work by the operator aiming the sight (similar to military optics) at the reg plate of the vehicle. Then they have to pull the trigger and the laser fires an invisible (to human eye) laser which reflects back off the reg plate or lights and the laser gun measures the time it takes for the laser to leave the gun and return. The screen on the gun will give a + or - indicating if the vehicle is travelling towards or away from the operator.
They are very accurate and can pick up vehicles from well over a mile. Basically, If you can see it with your eyes then you can get a speed off it.
For the OP, if the copper didn’t pull you over then chances are you’re not going to hear anything. There is a slim chance that he may have recorded your reg plate and will send a notice of intended prosecution (NIP) through the post but at that kind of speed it’s not worth it. I wouldn’t be worrying about it.
Mobile camera vans / cars / bikes work on a similar principle but they obviously record video evidence too.
A big point to note is that it’s never too late to hit the brakes. Just because it takes less than a second for the copper to read your speed, it doesn’t mean that he / she has got you. The first thing they copper has to do is form an opinion that you are speeding, they will then use the device to corroborate that opinion. However, they don’t have to see you to form the initial opinion. Eg; They’re stood on the roadside and can hear a motorbike high revving and changing through multiple gears before it comes into sight.
Camera vans have little or no description and are used to make revenue. Traffic cops on the other hand are generally not out there to catch people doing 33 in a 30.
ringfur:
Get some C.D. discs on the window. Mount then so they move with the vehicle movement. Has worked several times for me.
Another urban myth.
The CDs actually give a bigger reflective target for the laser to return off.
You may also be aware of various laser jammers that you can fit to your vehicle. They pick up the laser signal and send a different one back making it hard for the laser device to lock on to your speed. The copper will then get an error signal on the device screen.
Great if you get away with it but coppers are wise to them now and if you get caught using one then you’ll find yourself in court for perverting the course of justice. That’s an offence which can land you some time in the big house. The CDs in the window trick could also be defined as attempting to pervert the course of justice.
goshow:
yourhavingalarf:
If you haven’t been caught speeding in the previous 3 years…You’ll get an offer of a speed awareness course. If you were doing 45 in a 40, you’ll be getting a ticket.
The margin is 6% not 10% +2 mph.
I agree with you, it ■■■■■
Nope, ACPO guidelines are still 10% + 2mph. However, you can still get done for speeding at anything above the limit. Most speedometers read high these days. This is to account for tyre wear etc. So if you’re showing 45 then you’re more than likely only doing 43 / 44 in a truck. Cars or more inaccurate.
The radar style speed gun has been obsolete for a good few years now. They were never that accurate and could often pick up other vehicle behind you or travelling in the opposite direction.
These days most forces use pro-laser 3 guns. They work by the operator aiming the sight (similar to military optics) at the reg plate of the vehicle. Then they have to pull the trigger and the laser fires an invisible (to human eye) laser which reflects back off the reg plate or lights and the laser gun measures the time it takes for the laser to leave the gun and return. The screen on the gun will give a + or - indicating if the vehicle is travelling towards or away from the operator.
They are very accurate and can pick up vehicles from well over a mile. Basically, If you can see it with your eyes then you can get a speed off it.
For the OP, if the copper didn’t pull you over then chances are you’re not going to hear anything. There is a slim chance that he may have recorded your reg plate and will send a notice of intended prosecution (NIP) through the post but at that kind of speed it’s not worth it. I wouldn’t be worrying about it.
Mobile camera vans / cars / bikes work on a similar principle but they obviously record video evidence too.
Retired copper told us, 10% +2 is a guideline. They will not bother you for 5 miles. To much trouble not enough speed. In theory they could do you.
Speed checkers are laser based these days, very accurate.
It was pro-laser 3 gun as it matches what goshow says.
Really thankful for all these info. Never knew how it works before this…