Wednesday 24th November 2004

New limits could treble offences

'Mean speed' policy designed to ratchet down limits, says campaigner

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Government thinking on speed limits has undergone a sea change. Interpreting the notion that most people drive to the conditions rather than the speed limit, it has proposed that local authorities set limits in local areas at  the average traffic speed. This means that, while half the drivers will be below it, half will exceed it.

The new draft policy, contained in a recently published draft of the Government's primary local speed limit setting advice, says:

"Practitioners' thinking has evolved since then and many have expressed concern that 85th percentile speed can be heavily influenced by excessive speeds travelled by a minority of drivers. Some Traffic Authorities have therefore adopted the use of Mean speeds in assessing what is an appropriate local speed limit, as they are felt to better reflect what the majority of drivers perceive as an appropriate speed for the road.

The Department shares this view and therefore recommends that mean speeds be used in future assessments of appropriate speed limits."

Founder of the Safe Speed road safety campaign Paul Smith said, "All around the world and for many decades, speed limits have been set in accordance with the speed of traffic at such a level that only the fastest few should be prosecuted. Research evidence shows that this is the safest and most effective way to set speed limits. There has been some erosion of this principle over the last decade, but the new document promises a far more restrictive regime. In future the Government intends that speed limits should be set at the average speed of traffic. This immediately means that half of all motorists will be exceeding the new speed limits."

Smith continued: "The effect of this will be a gradual ratcheting down of speed limits and far more motorists criminalised despite the fact that they will be driving at a safe and appropriate speed according to the conditions."

Smith explained the technical details. "Speed limits have long been set at the level not exceeded by 85 per cent of motorists. This is called 'the 85th percentile rule'. The new proposals abandon the 85th percentile rule and replace it with a 'mean speed rule'. This means that with a typical speed limit defined under the new scheme, 50 per cent of drivers will be exceeding the speed limit by definition.

"For over ten years now we have speed reducing speed limits and speed cameras are spreading like a virus. The fact is this policy is comprehensively failing to reduce road deaths, yet the Government sticks stubbornly to its guns. They must be saying: 'The medicine isn't working! Let's increase the dose!'

"'Speed kills' road safety policy has become a dogma, encouraged by a series of vested interests. It isn't working and must be abandoned.

"Every rational person knows that 'The competent and careful actions of a majority of responsible people should obviously be considered legal.' Yet with speed limit laws, applied over-zealously we are criminalising the vast majority - and the government proposes to make it worse."

It's worth noting too that the result of a plethora of limits is bound to result in considerable confusion, extra workload on the police -- or more cameras.

The reason for the change is set out in the document DfT Circular x/05 Setting Local Speed Limits (see link below) as follows:

"There have been a number of important changes regarding speed limits and measures to control vehicle speeds, as well as further research to extend knowledge of the relationship between speed and the risk of collision and severity of injury. It is also known that there is a lack of understanding by a small number of road users about which speed limits are applied to particular types of road, and why.

"We are now circulating the proposed revised guidance. I would like to offer you an opportunity to comment. This guidance will apply in England only. The department is calling for responses by 15 February 2005."

Document is here: www.dft.gov.uk/

[mybrainhurts]

What link?

[whoateallthepies]

Are this lot starting to take the p*ss or what now? It's time to start voting with our feet and get rid of these condescending, patronising imbeciles who are drowning the country in their lies.

I never thought I would vote anything but Labour (It's a cultural requirement round here), but I have changed my mind. As long as we allow these cretins to ruin our country I will abstain.

It is time we started using the ridiculous amount of revenue collected from ALL of us to persecute REAL criminals, instead of letting them get away with whatever they want because the bleeding heart liberals say that they came from a broken home, and let them off. They need to spend money on police officers instead of advertising and cameras!!!

I don't see how driving at 35mph makes me a criminal mastermind. I only tend to drive over the limit when the kids aren't in the car, and often this is at 2.30am when I am on the way home from work and there are few cars on the road. If you don't drive everywhere at 50mph at that time, you end up with a taxi in your boot!!!

Rant over (for now)

[andrews]

I'm hoping that my snooper s4 and difusser will help save my license, I've always been law abiding but feel now that I've got to deploy potentially illegal technology to safeguard my license and livelihood - wonder when matt black will be a paint option for cars for max Infra red absorbtion

[count duckula]

Vote labour out.
what complete dribble.


Malc

[tonytonitone]

I'll will be voting against them as well.. for the first time.

[bar555]

I still feel the motorists are an easy target for the government to collect useful cash. I agree on driving 3-4 mph over the limit should not me a law-breaking citizen. Before they start printing out those NIP to the motorists, there should be more money spend on the police for serious crime or anti-socials. To improve a road safety is not banning the motorists - to give proper education to the new drivers and improve the road conditions.

>> Edited by bar555 on Wednesday 24th November 10:54

[mondeoman]

Get used to it, the car is public enemy number one for the totalitarian control freaks, as it gives the "people" too much freedom, and that is not acceptable to them.

Storming of the barricades a la Ukraine anyone?

[pete]

If they're really using mean speeds, the assertion that 50% of drivers will be above the limit and 50% below is based on a very flawed assumption, and a pretty ropey grasp of statistical analysis!

*Median* speed would imply this, but mean is influenced by the distribution of speeds. Work a simple example out for yourself - if 9 drivers drive a road at 25mph, but one drives it at 50mph, the mean speed is 27.5mph...

It's no wonder the government won't listen to the safe speed lobby!

Pete
(I'll get my coat)

>> Edited by pete on Wednesday 24th November 11:19

[Jasper Gilder]

I'm thinking of employing a man with a red flag.....

[big rumbly]

The 85th percentile rule has been around for ever. Why? Because it was implemented by the Ministry of transport who had real traffic engineers on board.
Nowdays any local local council official can call themselves a traffic engineer, although they have had no formal training in this area, and only react to the current fashionable thinking.
Ugh!

[safespeed]

pete said:

If they're really using mean speeds, the assertion that 50% of drivers will be above the limit and 50% below is based on a very flawed assumption, and a pretty ropey grasp of statistical analysis! *Median* speed would imply this, but mean is influenced by the distribution of speeds. Work a simple example out for yourself - if 9 drivers drive a road at 25mph, but one drives it at 50mph, the mean speed is 27.5mph... It's no wonder the government won't listen to the safe speed lobby! Pete (I'll get my coat)

Since the distribution of speed approximates to normal distribution the mean approximates to the median. It's hard enough to explain the basics to journalists without introducing another layer of complexity.

The mean speed will usually be around 6 to 8mph lower than than the 85th percentile speed on typical NSL roads (excluding country lanes).

[JamieT]

pete said:

If they're really using mean speeds, the assertion that 50% of drivers will be above the limit and 50% below is based on a very flawed assumption, and a pretty ropey grasp of statistical analysis! *Median* speed would imply this, but mean is influenced by the distribution of speeds. Work a simple example out for yourself - if 9 drivers drive a road at 25mph, but one drives it at 50mph, the mean speed is 27.5mph... It's no wonder the government won't listen to the safe speed lobby! Pete (I'll get my coat) >> Edited by pete on Wednesday 24th November 11:19

Yep, the last time I did statistics was 15 years ago at school, but even I spotted that mistake.

Edited to add: I'll take your word on it then Paul.

>> Edited by JamieT on Wednesday 24th November 11:49

[jacko lah]

JamieT said:

pete said: If they're really using mean speeds, the assertion that 50% of drivers will be above the limit and 50% below is based on a very flawed assumption, and a pretty ropey grasp of statistical analysis! *Median* speed would imply this, but mean is influenced by the distribution of speeds. Work a simple example out for yourself - if 9 drivers drive a road at 25mph, but one drives it at 50mph, the mean speed is 27.5mph... It's no wonder the government won't listen to the safe speed lobby! Pete (I'll get my coat) >> Edited by pete on Wednesday 24th November 11:19 Yep, the last time I did statistics was 15 years ago at school, but even I spotted that mistake.

Currently using the differences between mean and median to prove that my new assembly line is capable of 40 parts an hour as specified (the median is 41 an hour) and not the 32 an hour which the production manager says (the mean of 32 per hour is affected by unexplained 3, 4 or 5 minute stoppages, which may include the operator going walkabout, running out of components, or a genuine machine stoppage)

Back to the point ? Set a speed limit based on an experts view of risk.

20 outside a school
30 built up area
40 built up main road
60 single carriage way A/B main road
70 dual carriage way.
70 motorway
110 motorway not raining

and then if there's a sharp bend or a junction, put a clear warning sign.

If you go by what 50% of the numpties do, the speed limit will be :

40 past school
50 built up area
50 built up area main road
30 unlit country B road
45 unlit country A road
95 Motorway in the FOG.

[Lone Granger]

jacko lah said:

JamieT said: pete said: If they're really using mean speeds, the assertion that 50% of drivers will be above the limit and 50% below is based on a very flawed assumption, and a pretty ropey grasp of statistical analysis! *Median* speed would imply this, but mean is influenced by the distribution of speeds. Work a simple example out for yourself - if 9 drivers drive a road at 25mph, but one drives it at 50mph, the mean speed is 27.5mph... It's no wonder the government won't listen to the safe speed lobby! Pete (I'll get my coat) >> Edited by pete on Wednesday 24th November 11:19 Yep, the last time I did statistics was 15 years ago at school, but even I spotted that mistake. Currently using the differences between mean and median to prove that my new assembly line is capable of 40 parts an hour as specified (the median is 41 an hour) and not the 32 an hour which the production manager says (the mean of 32 per hour is affected by unexplained 3, 4 or 5 minute stoppages, which may include the operator going walkabout, running out of components, or a genuine machine stoppage) Back to the point ? Set a speed limit based on an experts view of risk. 20 outside a school 30 built up area 40 built up main road 60 single carriage way A/B main road 70 dual carriage way. 70 motorway 110 motorway not raining and then if there's a sharp bend or a junction, put a clear warning sign. If you go by what 50% of the numpties do, the speed limit will be : 40 past school 50 built up area 50 built up area main road 30 unlit country B road 45 unlit country A road 95 Motorway in the FOG.

you know what they say - the law is an ass - maybe its time we hit it with a stick to wake it up...??!

[RickH]

So is this a flexible speed-limit, or a new fixed one?

How often would they re-assess the limit? If it's a one time assessment, what you need to do is (assuming an appropriate location) get a like minded group of people together to drive past the assessment point at a suitably elevated speed so that the speed-population is distributed around a relatively high mean. They set the new speed-limit and everyone is happy.

[havoc]

safespeed said:

Since the distribution of speed approximates to normal distribution the mean approximates to the median. It's hard enough to explain the basics to journalists without introducing another layer of complexity. The mean speed will usually be around 6 to 8mph lower than than the 85th percentile speed on typical NSL roads (excluding country lanes).

And on country lanes the limit will drop to a rigourously enforced 45 to accomodate all those numpties who can't deal with anything other than nice straight roads with kerbs!!!

[funkihamsta]

Sorry l am confused:
"Smith explained the technical details. "Speed limits have long been set at the level not exceeded by 85 per cent of motorists. This is called 'the 85th percentile rule'."

The 85 percentile is the speed below which 85% of drivers travel at. It is not the speed at which official limits are set, as we know this to be a lie. Thus a speed limit is nothing to do with the 85% as it is set independently. Am l right?

The reason l asked this, is someone (a traffic planner) basically said this very exact thing only last friday. I guess the brain implant update must have been sent out at around the same time..

I pulled him up on this and he changed his story to how l understand it. (above).

[echo]

This story seems to be confused and is full of inconsistencies?

[funkihamsta]

Quote: "37. Circular 1/93 advised the use of 85th percentile speed to
determine local speed limits. This refers to the speed at, or below,
which 85 per cent of the traffic is travelling. Viewed another way it
is the speed only 15 percent of drivers exceed."

Its ok l found the above in the circular thread. Note that l am correct. Do not assume any speed limit is based on the 85th percentile. It is merely an advisory (circular 1/93 - above) that a speed limit be based on the 85th percentile. The speed limit itself MIGHT also represent the 85th percentile but it is surely unlikely given the politicisation of speed limits generally.

[Peter Ward]

I think that many speed limits were originally based on the 85% rule, but that most newer ones are politically set. I don't know whether the original 70 m'way limit was an 85% or a political one? Either way, I would guess that 85% on a m'way now would be nearer 90 than 70, but I don't expect that change.

But in reality this new approach -- strangely not trumpeted in the Queen's speech, probably due to lack of time wading through other civil liberty infringements -- is quantifiably different. You can be sure it won't be used to increase limits, just decrease them. In a current 40 limit, for example, the average speed is likely to be less than 40 so the limit will be "rounded down" to 30.

I recall a successful appeal regarding MOT tests a few years ago. The guidelines said that any exhaust noise above the "average" for that type of car should be failed. It was pointed out that this would eventually reduce the acceptable level to zero. That's what's now happening with speed limits, but this time with no appeal.