10% +2 mph rule
Discussion
This has probably been done before but with a few of my mates being done recently at relitively low speeds (58 in a 50 and 35 in a 30) does the old rule of "limit + 10% + 2mph" (i.e 35 in 30, 79 in 70 etc) still apply?
I have not seen it mentioned for a while.
I always thought it was a discretionery advisory tolerance and that they can still get you technically at anything above the limit but it was never usually the case.
I have not seen it mentioned for a while.
I always thought it was a discretionery advisory tolerance and that they can still get you technically at anything above the limit but it was never usually the case.
Can't remember the name.Don't quote me on this, but I thought that the 10% rule was there because speedometers by and large are not 100% accurate, so by law there must be no more than a 10% tolerance i.e. if you drive with the needle pointing exactly at 30mph, your acutal speed can be anywhere in the 27-33mph range. It would follow then that the +2mph rule would be there just in case you couldn't hold your speedo exactly at 30.
Wasn't this the explanation put forward when there was a drive for "zero tolerance" (getting done for 30.01mph in a 30 zone) a few of years ago?
Wasn't this the explanation put forward when there was a drive for "zero tolerance" (getting done for 30.01mph in a 30 zone) a few of years ago?
Teppic said: Wasn't this the explanation put forward when there was a drive for "zero tolerance" (getting done for 30.01mph in a 30 zone) a few of years ago?
So I'll quote you...
I believe this was indeed the case. In fact I remember a post from a police officer saying that this used to be the exact method employed. These days however I don't think that that holds true at all. Zero tolerance is a reality on a capricious, random basis.
If they want to do you for 31mph and your speedo was reading 29mph legally its your tough sh*t I expect...
I'm sure madcop has posted on this issue before...
You will not be prosecuted for 31 mph in this country.
Speedos have to be within 10% accuracy and can over read but not under read.
This allows you a tolerance under the current ACPO guidelines of 10% inacuracy of the speedo and 2 mph as a buffer to take up any inacuracy of the reading taken.
If your speedo is vey accurate, then you will get away with travelling at under 35mph registered on your speedo. If your speedo is inaccurate to the 10% rule, then you will be actually travelling at 27 mph when the speedo reads 30 mph. If you increase your speed to 30mph then you will be reading 33mph and if you increase your speed to 34 mph, then correspondingly, your speedo will be reading 37.5 mph or thereabouts (if my maths are correct) and it will give you the impresio that you can drive through the limit at well over the target set to activate it.
In my experience, most modern car speedos are mostly accurate until you start to exceed 90 mph. They get steadily more inaccurate the faster above 90mph the car is travelling. At 130mph shown on the speedo, they are often only travelling at about 122mph in reality.
Speedos have to be within 10% accuracy and can over read but not under read.
This allows you a tolerance under the current ACPO guidelines of 10% inacuracy of the speedo and 2 mph as a buffer to take up any inacuracy of the reading taken.
If your speedo is vey accurate, then you will get away with travelling at under 35mph registered on your speedo. If your speedo is inaccurate to the 10% rule, then you will be actually travelling at 27 mph when the speedo reads 30 mph. If you increase your speed to 30mph then you will be reading 33mph and if you increase your speed to 34 mph, then correspondingly, your speedo will be reading 37.5 mph or thereabouts (if my maths are correct) and it will give you the impresio that you can drive through the limit at well over the target set to activate it.
In my experience, most modern car speedos are mostly accurate until you start to exceed 90 mph. They get steadily more inaccurate the faster above 90mph the car is travelling. At 130mph shown on the speedo, they are often only travelling at about 122mph in reality.
robp said: Interesting stuff.
I suppose the easiest way to check your speedo is with the distance markers on the motorway?
That's right. Drive along at an indicated 130mph, concentrating on the little markers by the side of the BANG!!!! straight into the back of a caravan. Still, it's one less caravan, isn't it?
miniman said:
robp said: Interesting stuff.
I suppose the easiest way to check your speedo is with the distance markers on the motorway?
That's right. Drive along at an indicated 130mph, concentrating on the little markers by the side of the BANG!!!! straight into the back of a caravan. Still, it's one less caravan, isn't it?
robp said: BANG!!!! straight into the back of a caravan. Still, it's one less caravan, isn't it?
Reminds me of a time that I was driving up the M6 & I was just finishing a rant about caravans - how they didn't deserve to live & how we should be allowed to blow them up on sight etc to my (nervous) passenger, who had cadged a lift with me. We came round a bend in the motorway & were the first on scene to some numptie who had spun & turned their caravan into matchsticks (the towing car was on it's roof
) My passenger turned to me, white as a sheet & said "remind me not to annoy you in future"
madcop said: You will not be prosecuted for 31 mph in this country.
Even in a 20 limit !!!
Scamera guide is not to install unless 85 percentile is speed + 10% + 2mph, and camera usually set for this. You can be prosecuted for less than this, but unusual.
Would dispute madcop that most modern speedos are accurate. Happen to have an IRS certified one fitted, (i.e. admissable as evidence - as fitted to traffic cars) and most modern cars are still quite inaccurate, especially performance cars, ironically. RS and SRi drivers tending to think they are blasting along at 80 are often barely breaking 70. At high speed, then sheer scandalous. Following a fellow in a Cossie who thought he was flat out, showing 150, reality a mere 136. Can't really say where, right to silence and all that, but if Fife tourist Board knew they could rival Silverstone on GP day.
Speedos - they don't do what they say on the tin.
I wonder if this innaccuracy is anything to do with marketing and claimed top speeds?So does that mean my speed limiter which is supposed to be set at 155mph would show up as 170mph on the clock?
Is that why no matter how fast I try to average on the motorway (i.e. 85mph for 60 minutes solid with no slowing down) the average speed seems to be 40mph.
I noticed that the dash clock was 5% out a while ago when I did a little calibration test between the clock and the on-board computer display. I drove at a steady 70mph on the clock for 10 minutes and then checked the computer display. The OBC displayed 66.4 mph, hence 5% (well 5.x) out.
Unfortunately I now travel round with this in mind end end up passing everyone at Gatso sites as they slam on from 75 (really less than 70) to under 70 (more like 60) and I sail past at almost exactly 70.
Is that why no matter how fast I try to average on the motorway (i.e. 85mph for 60 minutes solid with no slowing down) the average speed seems to be 40mph.
I noticed that the dash clock was 5% out a while ago when I did a little calibration test between the clock and the on-board computer display. I drove at a steady 70mph on the clock for 10 minutes and then checked the computer display. The OBC displayed 66.4 mph, hence 5% (well 5.x) out.
Unfortunately I now travel round with this in mind end end up passing everyone at Gatso sites as they slam on from 75 (really less than 70) to under 70 (more like 60) and I sail past at almost exactly 70.
bobthebench said:
madcop said: You will not be prosecuted for 31 mph in this country.
Even in a 20 limit !!!
In my force area, 20 limits are usually very short stretches (unless they are in the middle of town centres) and policy is that enforcement will not be carried out within those limits.
Evidence of excess speed in the result of a collision though will be gathered and if the speed calculated by accident investigators is 31 in a 20 limit after such circumstcnes, then I expect the driver will receive a summons.
31mph in a 30mph limit will not be prosecuted as the marguin for error is very slight at that speed differential.
Scamera guide is not to install unless 85 percentile is speed + 10% + 2mph, and camera usually set for this. You can be prosecuted for less than this, but unusual.
Would dispute madcop that most modern speedos are accurate. Happen to have an IRS certified one fitted, (i.e. admissable as evidence - as fitted to traffic cars) and most modern cars are still quite inaccurate, especially performance cars, ironically. RS and SRi drivers tending to think they are blasting along at 80 are often barely breaking 70. At high speed, then sheer scandalous. Following a fellow in a Cossie who thought he was flat out, showing 150, reality a mere 136. Can't really say where, right to silence and all that, but if Fife tourist Board knew they could rival Silverstone on GP day.
Speedos - they don't do what they say on the tin.
In my experience modern cars are fairly accurate up to around the 90 mark where they steadily decline from true speed in error of greater speed shown on the speedo. The higher the speed shown, the greater the error between that and the true speed.
The reason for this is that occasionally, panda cars that have been used to follow speeders and the officers doing the check report offenders for excess speed, have to be checked for their reliabilty by running a check against VASCAR or a following check by a calibrated IRS job. My experience of this is that they are mostly unreliable over 90mph.
My Ford Mundano's speedo over read's by about 10MPH if the speedo show's 80 the GPS is indicating 72 90=82 and so on. The porker stay accurate to well over double the legal limit!!
Makes me wonder if the ford has really covered the miles it indicates or is it 10% less? It did explain why at a steady 80mph I was getting so many miles to the gallon though
Makes me wonder if the ford has really covered the miles it indicates or is it 10% less? It did explain why at a steady 80mph I was getting so many miles to the gallon though
The only way you can check your vehicles speedo is to put it on a rolling road or to find the place where there is a marked measured mile. These are usually either on motorways between two junctions that are close together or on dual carriageway roads.
They are identifiable by looking for the markers which are circular tin plates. There will be 5 of them and they are coloured thus.
1st in line yellow
2nd in line 3/4 yellow with a quarter red
3rd in line 1/2 yellow 1/2 red with vertical division between halves.
4th in line 3/4 red with a quarter yellow
5th in line all red.
These markers are about 2 feet high and about 9 inches diameter and are usually fixed to the verge adjacent to the hard shoulder. they are sometimes fixed in the central reservation.
To check the speedo accurately, Police use a calibrated stop watch and get the car to 60mph prior to passing the first marker. On passing the second, the passenger/observer activates the stop watch and the driver maintains a steady 60mph until he reaches the last red marker. as the vehicle passes the red marker, the stop watch should obviously read 1 minute.
There are measured miles between junctions 6 and 7 and 11 and 12 on the M4 and also on the A 413 Amersham bypass as you go out of Old Amersham past Shardlows Manor towards Great Missenden.
They are identifiable by looking for the markers which are circular tin plates. There will be 5 of them and they are coloured thus.
1st in line yellow
2nd in line 3/4 yellow with a quarter red
3rd in line 1/2 yellow 1/2 red with vertical division between halves.
4th in line 3/4 red with a quarter yellow
5th in line all red.
These markers are about 2 feet high and about 9 inches diameter and are usually fixed to the verge adjacent to the hard shoulder. they are sometimes fixed in the central reservation.
To check the speedo accurately, Police use a calibrated stop watch and get the car to 60mph prior to passing the first marker. On passing the second, the passenger/observer activates the stop watch and the driver maintains a steady 60mph until he reaches the last red marker. as the vehicle passes the red marker, the stop watch should obviously read 1 minute.
There are measured miles between junctions 6 and 7 and 11 and 12 on the M4 and also on the A 413 Amersham bypass as you go out of Old Amersham past Shardlows Manor towards Great Missenden.
Captain Muppet said:
bobthebench said: ...Happen to have an IRS certified one fitted, (i.e. admissable as evidence - as fitted to traffic cars) ...
Where can I get one of those certified speedos?
could be fun folowing the local MP`s and cheif supers car with one.
>> Edited by outlaw on Wednesday 12th March 11:21
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