Speed limits speedometers vs GPS speed

[Armitage.Shanks]

There's a reason the (as then) ACPO Guidelines of 10%+2 were used, it was because if they didn't set some sort of tolerance the processing system would become overloaded and they wouldn't be able to cope with administering them.

There's a human element to producing and processing the tickets against a set timeframe - NIP 14 days etc. and processing speeding offences at 1-2mph above the posted limit would break the system. There was also a 'concern' of criminalising drivers the majority of whom are generally law-abiding citizens hence the devised option and subsequent increase in speed awareness courses.

[BertBert]

I was under the impression, probably wrongly that they had a different origin. I thought they were originally guidelines to officers. Under 10% + 2 officers had discretion whether they gave a ticket. Over the threshold they didn't.

[PorkInsider]

giantdefy said:

Super Sonic said:

Sorry but you're wrong. The guidelines are exactly that, so saying they 'wouldn't be allowed under the guidelines' is clearly nonsense. If it wasn't allowed, they would be rules, not guidelines.
Are you trying to claim police always follow guidelines?

What is being said is we have never seen any documentary evidence of the guidelines not being followed

And I'm almost certain that AGTlaw previously challenged anyone who said otherwise to produce documentary evidence of action commencing for a speed below the thresholds.

I certainly recall him posting responses he'd received from police forces when he requested them to disclose if they do or don't follow the guidelines, and whether they have ever issued tickets outside those guidelines which weren't subsequently cancelled.

I'm inclined to think a renowned motoring law barrister would have a good handle on this stuff.

[Armitage.Shanks]

BertBert said:

I was under the impression, probably wrongly that they had a different origin. I thought they were originally guidelines to officers. Under 10% + 2 officers had discretion whether they gave a ticket. Over the threshold they didn't.

Officers have discretion both over and under the limit. Where you're dealing with a physical presence rather than an automated system that can't make decisions discretion is available. I'd suggest that anyone who decides to argue the toss and 'fail the attitude test' will not do themselves any favours be processed accordingly whether or not the speed is under the guidelines.

It's all about moderating someones behaviour, educating and reducing risk of future 'offending'. In this country police have the option of 'advice' taking into account all the salient factors at the scene that is lacking in most other countries.

[911hope]

blank said:

Not exactly.

It specifies tyre pressures 0.2 bar above the manufacturer's specified pressure (as it's a worse case to have tyres over inflated) and a temperature at the speedometer between 18 and 28 degC. Don't know why the temperature requirement is there but possibly due to old school mechanical speedos that would behave differently if very cold (or hot).

Boyle's law.

[BertBert]

Armitage.Shanks said:

Officers have discretion both over and under the limit. Where you're dealing with a physical presence rather than an automated system that can't make decisions discretion is available. I'd suggest that anyone who decides to argue the toss and 'fail the attitude test' will not do themselves any favours be processed accordingly whether or not the speed is under the guidelines.

It's all about moderating someones behaviour, educating and reducing risk of future 'offending'. In this country police have the option of 'advice' taking into account all the salient factors at the scene that is lacking in most other countries.

Have or had?

[FiF]

Zarco said:

blank said:

This is being massively over complicated!!

Easiest thing to do is next time you're on a nice straight flat road, compare GPS speed to your speedo for a few different speeds, then use that as your "calibration" for your own car.

Your speedo is a much better live readout than a phone GPS once you know how it behaves compared to true speed.


If anyone wants to spend a couple of grand having this done professionally with 100Hz IMU blended and RTK corrected GPS then feel free to PM me. The result will be the same.

Absolutely this is the simplest and quickest way to sort it. The GPS engines in phones and the like aren't up to providing proper speed data logging in anything other than the simplest situation, but as described above, straight flat road and checking the difference at various steady speeds is for most people quite sufficient to produce a correction chart across the typical range.

Thankfully no longer have to mess about finding the official measured miles.

[Derek Smith]

douglasb said:

The "10% plus" doesn't vary from region to region and nobody on here (or anywhere else as far as I am aware) has ever been able to show any paperwork for being charged at a speed of anything under limit + 10% +2mph (the starting point for charging) . Of course it happened to a friend's brother's aunt 17 years ago and she didn't keep the letter...

GPS receivers aren't bolted to buildings. As GPS stands for Gobal Positioning by Satellite, there's a clue in the name of where the signals come from. The receiver in the vehicle needs to receive signals from (I think) 3 satellites to get a "fix". The more satellites it can "see" the more accurate the indicated speed will be. However as the GPS doesn't measure an instantaneous speed but calculates the speed based on the time to travel a measured distance in a measured time the speed is going to be an average. Of course, if you are doing a steady speed on a straight and flat road and the distance/time measurement happens every second then the GPS speed is going to be pretty much the same as the actual speed in that second but a longer period of time to measure the distance travelled could make the GPS speed less accurate and doing 0-60 in 3 seconds will also mean that the indicated GPS speed is meaningless. As has also been said, if the road isn't straight the GPS only measures the distance/time between two points so assumes that you have gone between them in a straight line so this could underestimate your actual speed if there is a shrap bend involved.

Most speed cameras these days are laser and aren't averaging a speed measurement (well they are, but with thousands of measurements taken in 0.3 of a second and with the device rejecting readings that are out of a certain tolerance they can be regarded as instantaneous readings).

A speedomter is not allowed to under-read the speed but can over-read by up to 10%. There is a load of rubbish sometimes posted that says "If you were caught at 60 in a 50 your speedo must have been reading 66". That used to be the case but from my experience with cars from the last 20 years I think that speedomters over-read by a couple of mph and this is consitent throughout the speed range rather than being a perceontage above the actual speed as it may have been in the past.

There is no 'rule' with regards the threshold for prosecution for speeding. ACPO, as was, issued guidelines.

I was prosecutions inspector in my force and we used it as a rule as long as there were no aggravating factors. In other words, if an officer wanted to prosecute a driver at a speed lower than the advised limit, they had to produce reasons. In the 2 years or so I was a prosecutions inspector, I can remember two instances, both instigated by traffic officers - one of which was when the errant driver overtook a police car at over the limit, the other when the driver would not accept she was over the limit - and both went through to CPS. They came back to me both times and I justified the limit. There may have been more as memory fades. I can't 'produce paperwork' to support, but even if I could, I wouldn't. If you don't want to believe me, then by all means don't. Believe your own fairly stories.

I have had no acquaintance, relative or friend who has told me they have been prosecuted for a speed under the guidelines.

[agtlaw]

PorkInsider said:

And I'm almost certain that AGTlaw previously challenged anyone who said otherwise to produce documentary evidence of action commencing for a speed below the thresholds.

I certainly recall him posting responses he'd received from police forces when he requested them to disclose if they do or don't follow the guidelines, and whether they have ever issued tickets outside those guidelines which weren't subsequently cancelled.

I'm inclined to think a renowned motoring law barrister would have a good handle on this stuff.

I’ve seen thousands of ‘speeding tickets’ from all forces in England. One was 52/50 mph but that was very unusual circumstances (linked to a PCJ case) and dropped when a NG plea was entered. Every other ‘ticket’ was at least 10% + 2 mph over the limit.

I wrote to one force to get enforcement thresholds via a FOI. Various journalists have written to multiple police forces and published FOI responses.

[agtlaw]

Derek Smith said:

I was prosecutions inspector in my force and we used it as

Was that in the 1970s?

[Derek Smith]

agtlaw said:

Derek Smith said:

I was prosecutions inspector in my force and we used it as

Was that in the 1970s?

?

[BertBert]

agtlaw said:

I’ve seen thousands of ‘speeding tickets’ from all forces in England. One was 52/50 mph but that was very unusual circumstances (linked to a PCJ case) and dropped when a NG plea was entered. Every other ‘ticket’ was at least 10% + 2 mph over the limit.

I wrote to one force to get enforcement thresholds via a FOI. Various journalists have written to multiple police forces and published FOI responses.

Just curious on your view. If a speedcam one somehow came through, say 77 in a 70 and went to court under a NG plea. Assuming the evidence was sound, would it succeed?

[agtlaw]

Derek Smith said:

agtlaw said:

Derek Smith said:

I was prosecutions inspector in my force and we used it as

Was that in the 1970s?

?

1970s

[ATG]

Craig_suke said:

E-bmw said:

Why is it that so many people on here get all hung up on whether anyone did or didn't get a ticket for doing under or over the "guidelines" stated?

I personally couldn't give 2 sh!ts what speed anyone did or didn't get done for or whether it is concocted or not, and I certainly couldn't be bothered with giving the claimant any grief or need for proof.

If it happened it happened, if it didn't it didn't what is the point in arguing the point?

Build a bridge & get over it.

Personally find it’s funny that people will try to pass around false information, these people need to be called out about it

I’ll put it out there that no forces ticket office (the ones who would issue the ticket or offer a course) would accept a ticket for less than their own stated guidelines as it would be an easy argument in court. The officers, camera’s and vans all operate to these guidelines.

As mentioned many times people claim it to get some attention but then could strangely prove it.

You think "I wasn't breaking the law enough to be prosecuted" is a defence? Interesting.

[BertBert]

ATG said:

You think "I wasn't breaking the law enough to be prosecuted" is a defence? Interesting.

Au contraire Rodney. There is a view on here that a ticket under 10%+2 wouldn't succeed, which I don't share.

[agtlaw]

ATG said:

You think "I wasn't breaking the law enough to be prosecuted" is a defence? Interesting.

That actually worked in Marrable (2020). Charged with exceeding a 50 mph limit. Prosecution alleged 72 mph. Marrable's defence was - "my GPS said 53-54 mph." Acquitted at trial and acquittal upheld on appeal to the Divisional Court.

[OutInTheShed]

In the old days, when more speeding offences were 'detected' by methods like VASCAR, there were often significant measurement errors.
Hence the need for a tolerance between 'observed speed' and the legal limit.

People prosecuted for doing 40 might only have been doing 35.

[MustangGT]

BertBert said:

ATG said:

You think "I wasn't breaking the law enough to be prosecuted" is a defence? Interesting.

Au contraire Rodney. There is a view on here that a ticket under 10%+2 wouldn't succeed, which I don't share.

I think the whole point is a ticket for less than 10%+2 would not be issued.

[ATG]

agtlaw said:

ATG said:

You think "I wasn't breaking the law enough to be prosecuted" is a defence? Interesting.

That actually worked in Marrable (2020). Charged with exceeding a 50 mph limit. Prosecution alleged 72 mph. Marrable's defence was - "my GPS said 53-54 mph." Acquitted at trial and acquittal upheld on appeal to the Divisional Court.

Was that decision based on the prosecution's evidence being unreliable rather than a happy consensus being achieved that he was indeed speeding, but not by much?

[ATG]

MustangGT said:

BertBert said:

ATG said:

You think "I wasn't breaking the law enough to be prosecuted" is a defence? Interesting.

Au contraire Rodney. There is a view on here that a ticket under 10%+2 wouldn't succeed, which I don't share.

I think the whole point is a ticket for less than 10%+2 would not be issued.

That might well be true, but the question is whether the "I only broke the law a bit" defence is likely to succeed. Like Bert^2, that seems a rather strange idea to me.