speed limits: do they work? (of course not)

[anthonym]

V8 Fettler said:

The Principal Designer (was CDM-C)

Interesting, who is that?

[anthonym]

quote "The Principal Designer (was CDM-C) should pick up on your adverse design risk assessments and stop the process. Barriers adjacent to the road create other issues, as I'm sure you are aware." end quote



ok think I found it, is this it? edit: this doc is stamped DRAFT.

https://www.citb.co.uk/documents/cdm%20regs/indust...

[PDF]Industry guidance for Principal Designers - CITB
https://www.google.ch/url?sa=t&rct=j&q=&am... Advice for principal designers working for domestic clients 15 ... There are six guides: one for each of the five duty holders under CDM and an additional one for workers. .... For further information on the health and safety file, see Annex C.
[PDF]

Edited by anthonym on Wednesday 19th August 13:24

Edited by anthonym on Wednesday 19th August 13:25

[anthonym]

vonhosen said:

robinessex said:

The late L J K Setright, probably the most intelligent motoring journalist ever, said there should be only 1 motoring offence, dangerous driving.

Many probably more intelligent people don't agree with him.

The purpose of a speed limit is to provide for the safety of all road users. To meet this purpose, a speed limit must be acceptable to the public and be enforceable by the police.

Currently the situation achieves neither.

[anthonym]

V8 Fettler said:

The (historical) role of Co-ordinator under the "Construction (Design and Management) Regulations" included "advise on the suitability, co-ordination and compatibility of designs in relation to health and safety."

The Co-ordinator's role has now been replaced, some background: http://www.designingbuildings.co.uk/wiki/CDM_2015_...

thanks for that. Were you saying in that earlier exchange that this role exists within the council structure and that person would have the power to stop the councillor enacting anything inappropriate, presumably based on established standards ?

Absolutely not trying to put words in your mouth here, merely hoping to understand the powers and processes in play.

[anthonym]

V8 Fettler said:

I'm not aware of any CDM Co-ordinator who is/was directly employed by a local authority, there would probably be a conflict of interest. CDM Co-ordinators had no powers of enforcement, neither do Principal Designers, but it could be professional suicide and financially disastrous for all parties to allow a high risk design to be developed when a low risk alternative was readily available, e.g http://www.hse.gov.uk/press/2010/coi-sw-739sww09.h...

The risks are generally highest during the construction phase of a project, but there should be consideration of risks applicable to use, maintenance and final demolition, the "use" bit being relevant to Opulent Bob's roundabout project.

as I try to think that through from that link (but in reverse order):

"Notes to editors
Section 3(1) of the Health and Safety at Work etc Act 1974 states: "It shall be the duty of every employer to conduct his undertaking in such a way as to ensure, so far is reasonably practicable, that persons not in his employment who may be affected thereby are not thereby exposed to risks to their health or safety."

are the parties in Opulent Bob's case thus:

employer=the council (i.e. Opulent Bob's employer)
persons not in his employment = road users (I suppose = other persons' employees and/or the public more generally) i.e. everyone regardless unless an employee

That informs me in that while I am aware of public liability, I have not thought of HSE matters in terms of road safety or indeed related to councils in that context. Seems obvious now you point it out - assuming I have understood correctly?

"While it is rare for designers to be charged with breaching health and safety legislation, they must be aware they can be held responsible where bad design is an important contributory factor to a work-place fatality."

The "designer" being "the council"? Though within the council we have those qualified to design, being usurped by a (unqualified) political master?


edit: our (Opulent Bob and me) above two posts posted simultaneously - had to smile at "left the country".

Edited by anthonym on Thursday 20th August 04:31

[anthonym]

gosh, India. Now that is a highway safety challenge. I was reading about their problems the other day. And hot! :-)

[anthonym]

OpulentBob said:

anthonym said:

gosh, India. Now that is a highway safety challenge. I was reading about their problems the other day. And hot! :-)

You might think that (I did!) - it's chaotic yes - but I saw my first actual traffic collision in 4 months this morning. A tiny, minor prang which just cracked a light cluster. How many times on a UK commute do you see the evidential spray of glass shards across a roundabout or the side of a road? Here, hardly ever.

Saying that, I'm not allowed to drive here. Had to sign a contract for my work/health insurance saying that I wouldn't drive, use a 2-wheeler, or cycle. And I'm glad for it. I'd crash in seconds... It's a totally different approach/mentality to driving here.

The car horns everywhere drive you mad. Like, to the point of developing a tick over them. Between about 6am and 2am, you'll be lucky if you go for 5 seconds without hearing a car horn. It reminds me of the South African World Cup and the bloody vuvuzela. "Look, we can make a noise, LET'S MAKE NOISE!!"

that no-drive term speak volumes - would suit some pressure groups. I used to live in a car free village (well, town really) and it was def relaxing - assuming I didn't fall off my bike in the snow :-)


edit: IIRC the statistic I saw was someone is killed every 4 minutes... enormous pop of course, but still.

Edited by anthonym on Thursday 20th August 06:41

Edited by anthonym on Thursday 20th August 06:42

[anthonym]

thanks flemke, interesting. Also vaguely connected to the op in that which was because I have slowly and dimly become aware of the powers that be complaining that their speed limits, enforcement and general measures of suppression are not working; indeed Plato (or similar I forget exactly who) commented on the futility of such behaviour by government - so it seems we never learn and history repeats. Then I started to delve into it all. Really quite surprising and depressing.

[anthonym]

Earlier in this thread evidence was requested about the 85th percentile etc.

Cirillo showed that Interstate speeds of 11 or 12 mph higher than the mean were the bottom of the risk curve. That puts the safest speed (safest by a very small margin) slightly above the 85th percentile - perhaps around the 90th. On surface highways, Solomon found the safest point about 5 mph above the mean, at or very close to the 85th speed.

Anthony

Ps I am not sure that discussion of this should not be a discussion in its own right because it is at the core of road safety and was not the thrust of my op.

[anthonym]

flemke said:

That is helpful, but please bear in mind that the data are not saying that 85th (or whatever) percentile speed is the "safest speed", per se. They are saying that the drivers who have chosen to drive at the 85th are the safest drivers. It is quite possible, I would say quite probable, that those same drivers would still be the safest if they were driving at the 65th or at the 95th.

Thus the question is probably not, "Why is 85th the safest speed?", but, rather, "Why do the safest drivers choose the 85th?"

Good question, I'll get back to you on that.

[anthonym]

this is just for late night readers in India (plus those not there who can't sleep) and not my considered response, however I found it interesting and moving in the direction of an informative answer:

copy begins

85/67th Percentile Speed

Defined as that speed at or below which 85 percent of the traffic is moving. On urban roadways the 85th percentile speed has been found to be the safest speed, where the 85th exceeds 50 mph the safest speed shifts to the 90th percentile. Speed limits established on the basis of the 85th percentile on urban roadways conform to the consensus of those who drive highways as to what speed is reasonable and prudent, and are not dependent on the judgement of one or a few individuals.

However, in no case should the speed limit be set below the 67th percentile speed of free flowing vehicles.

Determining The Safe For Conditions Speed

The traffic engineer's speed survey is simply a measurement of the "public's consensus" as to what free-flowing speed they have found to be safe. Each motorist drives at a speed they feel comfortable and safe with. Each driver expresses their comfort level by their actions, taking in to account all visual clues that may be present. Engineers have found this to be a better process than basing the speed limits on the arbitrary judgments of a few. Setting all traffic control devices, turn lane lengths etc. based on this measured public consensus has been the most effective in reducing accident rates.

copy ends

from year 2000.

it seems to suggest it is not the drivers who are safe, but the speeds themselves... I'm thinking about that: after all, the search is indeed for "the safest speed"...


and p.s. I share the views above about political interference. I think our engineers should be allowed to engineer.

Edited by anthonym on Saturday 22 August 03:10

[anthonym]

think I should have said "the safest speed LIMIT"...

I had an example of that bunching with smaller gaps only yesterday, the peloton of 4 cars with me at the back, all had gaps that were too small, one crash, all crash was my thought. I put the car in 2nd gear and left it there, which widened the gap and saved my brakes down the mountain (an Alp). Everyone else had their speed governed by the lead car which was not local. Once I found the need to brake suddenly or more suddenly that I would have preferred, which ordinarily never happens on that route - my mind was simply elsewhere.

[anthonym]

@flemke (edited to add this)

how about this from Michigan State Police:

copy begins

What is “85th Percentile Speed”?
• The speed that 85 percent of the vehicles are traveling at or below
• Ideal speed to set as the maximum limit:
– Provides the lowest speed variance between vehicles, and thus provides the lowest crash numbers
– Provides optimum enforceability • The SAFEST speed limit

copy ends

So while the 85th percentile (ibid) is not per se the "safest speed", it is the "safest speed limit". So I suppose that lower limits are by definition, not the safest speed limits regardless of driver skill

Does that work?

edit: the above absolutely allows for the "speed limit" and thus the 85th not being the safest speed since the speed limit is a maximum (with flexibility) indicator, not a statement of the speed everyone must travel at to be safe.- since all of us driving at 30mph in towns and villages would be ludicrous.

Edited by anthonym on Saturday 22 August 12:34

Edited by anthonym on Saturday 22 August 13:59

[anthonym]

flemke said:

anthonym said:

Earlier in this thread evidence was requested about the 85th percentile etc.

Cirillo showed that Interstate speeds of 11 or 12 mph higher than the mean were the bottom of the risk curve. That puts the safest speed (safest by a very small margin) slightly above the 85th percentile - perhaps around the 90th. On surface highways, Solomon found the safest point about 5 mph above the mean, at or very close to the 85th speed.

Ps I am not sure that discussion of this should not be a discussion in its own right because it is at the core of road safety and was not the thrust of my op.

That is helpful, but please bear in mind that the data are not saying that 85th (or whatever) percentile speed is the "safest speed", per se. They are saying that the drivers who have chosen to drive at the 85th are the safest drivers. It is quite possible, I would say quite probable, that those same drivers would still be the safest if they were driving at the 65th or at the 95th.

Thus the question is probably not, "Why is 85th the safest speed?", but, rather, "Why do the safest drivers choose the 85th?"

because to do otherwise would make the factors that make him safer disappear i.e. that is where safety resides and it is a moving target (if I can be forgiven for the pun as it seems rather apt)..


Happy to onward discuss that a bit.... more my thinking out loud:

drivers don't choose the 85th as such, they create it with their behaviour, they drive in the safest manner (i.e. least chance of KSI) and it turns out that this tends always to the 85th percentile (or whatever). So driving in some other percentile, isn't where drivers observe safety to be, it is where they see danger (another topic). If all those "safe 85th drivers" are driving in the 65th percentile (as derived in ideal conditions), it won't be the 65th, it will be the 85th. If they are forced into another percentile, then it is not the 85th and no longer safe.

For an attempt at clarity, as I understand it, the 85th (or whatever) (in ideal free flow conditions) is to determine the speed limit for maximum safety in said ideal free flow conditions (another discussion), so in only that instance the safe limit and the 85th (or whatever) are the same. In all other conditions (i.e. less than ideal) the 85th will not be the speed limit, it may even be where the 50th resides in ideal conditions, when conditions are no longer ideal, for example rain etc Drivers (we all) know when conditions are not ideal. It moves around and only in ideal conditions is it the speed limit (with grace), if the speed limit (with grace) was appropriately set.

of course we have multiple speed limits, variable speed limits and so on, but the above is the foundation I see.

What do you think?

Anthony



KSI = Killed or Seriously Injured

Edited by anthonym on Saturday 22 August 19:13

[anthonym]

flemke said:

anthonym said:

Earlier in this thread evidence was requested about the 85th percentile etc.

Cirillo showed that Interstate speeds of 11 or 12 mph higher than the mean were the bottom of the risk curve. That puts the safest speed (safest by a very small margin) slightly above the 85th percentile - perhaps around the 90th. On surface highways, Solomon found the safest point about 5 mph above the mean, at or very close to the 85th speed.

Anthony

Ps I am not sure that discussion of this should not be a discussion in its own right because it is at the core of road safety and was not the thrust of my op.

That is helpful, but please bear in mind that the data are not saying that 85th (or whatever) percentile speed is the "safest speed", per se. They are saying that the drivers who have chosen to drive at the 85th are the safest drivers. It is quite possible, I would say quite probable, that those same drivers would still be the safest if they were driving at the 65th or at the 95th.

Thus the question is probably not, "Why is 85th the safest speed?", but, rather, "Why do the safest drivers choose the 85th?"

because to do otherwise would make disappear the factors that make him safe(r).

long(er) answer is a few posts above here.

[anthonym]

flemke said:

anthonym said:

flemke said:

anthonym said:

Earlier in this thread evidence was requested about the 85th percentile etc.

Cirillo showed that Interstate speeds of 11 or 12 mph higher than the mean were the bottom of the risk curve. That puts the safest speed (safest by a very small margin) slightly above the 85th percentile - perhaps around the 90th. On surface highways, Solomon found the safest point about 5 mph above the mean, at or very close to the 85th speed.

Anthony

Ps I am not sure that discussion of this should not be a discussion in its own right because it is at the core of road safety and was not the thrust of my op.

That is helpful, but please bear in mind that the data are not saying that 85th (or whatever) percentile speed is the "safest speed", per se. They are saying that the drivers who have chosen to drive at the 85th are the safest drivers. It is quite possible, I would say quite probable, that those same drivers would still be the safest if they were driving at the 65th or at the 95th.

Thus the question is probably not, "Why is 85th the safest speed?", but, rather, "Why do the safest drivers choose the 85th?"

because to do otherwise would make disappear the factors that make him safe(r).

long(er) answer is a few posts above here.

I see the distinction you are making between "safest" speed and "safest" limit. As alluded to above by Toltec, the question then becomes, how is a limit set in the first place?
Implied in the "safest limit" axiom is that the safest limit for a given road will depend on the sociology of those driving on it.

what do we mean by "sociology"? I'm wary of assuming anything.

[anthonym]

flemke said:

anthonym said:

flemke said:

anthonym said:

flemke said:

anthonym said:

Earlier in this thread evidence was requested about the 85th percentile etc.

Cirillo showed that Interstate speeds of 11 or 12 mph higher than the mean were the bottom of the risk curve. That puts the safest speed (safest by a very small margin) slightly above the 85th percentile - perhaps around the 90th. On surface highways, Solomon found the safest point about 5 mph above the mean, at or very close to the 85th speed.

Anthony

Ps I am not sure that discussion of this should not be a discussion in its own right because it is at the core of road safety and was not the thrust of my op.

That is helpful, but please bear in mind that the data are not saying that 85th (or whatever) percentile speed is the "safest speed", per se. They are saying that the drivers who have chosen to drive at the 85th are the safest drivers. It is quite possible, I would say quite probable, that those same drivers would still be the safest if they were driving at the 65th or at the 95th.

Thus the question is probably not, "Why is 85th the safest speed?", but, rather, "Why do the safest drivers choose the 85th?"

because to do otherwise would make disappear the factors that make him safe(r).

long(er) answer is a few posts above here.

I see the distinction you are making between "safest" speed and "safest" limit. As alluded to above by Toltec, the question then becomes, how is a limit set in the first place?
Implied in the "safest limit" axiom is that the safest limit for a given road will depend on the sociology of those driving on it.

what do we mean by "sociology"? I'm wary of assuming anything.

The range of drivers whose speeds might be measured, in order to establish the percentiles, is not the same from one age or national cohort to another. There may well be other criteria across which there are differences, but of those two - age and nationality - I am sure.

For example, in England if one is traveling on an NSL single carriageway at 60 mph, catches up to a car driving at 45-50 mph, and overtakes that car, it is not uncommon that the overtaken driver will indignantly protest the overtake by a flashing of lights, etc.

That sort of hysteria does not happen on the Continent, where people do not take it as a personal insult that someone else wishes to travel at a faster speed than themselves.

For a given set of road conditions, I submit, a random selection of Italian or German drivers would drive faster than a random selection of English drivers would do. Even taken empirically from the driving behaviour itself, the 85th percentile will not be a constant.

ok, thanks for that clarification. (made me smile)

[anthonym]

anthonym said:

flemke said:

anthonym said:

flemke said:

anthonym said:

flemke said:

anthonym said:

Earlier in this thread evidence was requested about the 85th percentile etc.

Cirillo showed that Interstate speeds of 11 or 12 mph higher than the mean were the bottom of the risk curve. That puts the safest speed (safest by a very small margin) slightly above the 85th percentile - perhaps around the 90th. On surface highways, Solomon found the safest point about 5 mph above the mean, at or very close to the 85th speed.

Anthony

Ps I am not sure that discussion of this should not be a discussion in its own right because it is at the core of road safety and was not the thrust of my op.

That is helpful, but please bear in mind that the data are not saying that 85th (or whatever) percentile speed is the "safest speed", per se. They are saying that the drivers who have chosen to drive at the 85th are the safest drivers. It is quite possible, I would say quite probable, that those same drivers would still be the safest if they were driving at the 65th or at the 95th.

Thus the question is probably not, "Why is 85th the safest speed?", but, rather, "Why do the safest drivers choose the 85th?"

because to do otherwise would make disappear the factors that make him safe(r).

long(er) answer is a few posts above here.

I see the distinction you are making between "safest" speed and "safest" limit. As alluded to above by Toltec, the question then becomes, how is a limit set in the first place?
Implied in the "safest limit" axiom is that the safest limit for a given road will depend on the sociology of those driving on it.

what do we mean by "sociology"? I'm wary of assuming anything.

The range of drivers whose speeds might be measured, in order to establish the percentiles, is not the same from one age or national cohort to another. There may well be other criteria across which there are differences, but of those two - age and nationality - I am sure.

For example, in England if one is traveling on an NSL single carriageway at 60 mph, catches up to a car driving at 45-50 mph, and overtakes that car, it is not uncommon that the overtaken driver will indignantly protest the overtake by a flashing of lights, etc.

That sort of hysteria does not happen on the Continent, where people do not take it as a personal insult that someone else wishes to travel at a faster speed than themselves.

For a given set of road conditions, I submit, a random selection of Italian or German drivers would drive faster than a random selection of English drivers would do. Even taken empirically from the driving behaviour itself, the 85th percentile will not be a constant.

ok, thanks for that clarification. (made me smile)

I propose we modify the question from:

how is a limit set in the first place?

to

how is a limit BEST/IDEALLY/OPTIMALLY set in the first place?

I propose this because we know how limits are currently set (without wishing to start a debate about that in itself).

I further propose that the catch-22 matter of existing limits preventing free flow be left aside at this time to allow progress until that item is unavoidable.

How say you?

[anthonym]

aye, well I think there should be only one driving offence, which is "dangerous driving" (not going to happen of course); but I think like you I'd like to see where our discussion leads/takes us. I'll get back to you.

[anthonym]

flemke said:

anthonym said:

I propose we modify the question from:

how is a limit set in the first place?

to

how is a limit BEST/IDEALLY/OPTIMALLY set in the first place?

I propose this because we know how limits are currently set (without wishing to start a debate about that in itself).

I further propose that the catch-22 matter of existing limits preventing free flow be left aside at this time to allow progress until that item is unavoidable.

How say you?

Cool.

I myself think of speed limits as law that is bad in concept and, even if one were to think that it was good in concept, that nevertheless is badly enforced.

On that basis, I am not sure that I can offer much of an opinion on how speed limits ought to be set. Nonetheless I would be interested in what you and others think about this question.

I've been thinking about this and there isn't really a short answer to what is a complex and emotive issue. Emotive because of the KSI (killed and seriously injured) people and their loved ones who are affected.

I have here research that favours no speed limits at all, but I don' think we (not least me) are ready for that.

I also have masses of research into how to set limits and manage road safety generally.
Anything I write that is not reasonably comprehensive will be too easy to shoot to tatters, rightly so because it would be incomplete. Indeed anything I write won't be apt because I am a student of the subject and neither a teacher nor a researcher of it.

So what to do? In the next post to this I will post the comprehensive work that thus far I have found to cover the subject without being in book form and length. The problem is global and research across the world is all relevant.

I thought about just posting a link, but if I do (a) it risks breaking in the future and (b) I suspect it won't be read (much) and certainly will not form part of search results in PH.

There is one other set of words I think needs to go with this, which is Julie Cirillo's testimony to the Senate, not least as she, on my birthday in 2003 testified as to the continuing validity of Solomon's 1964 paper (referring to his 1963 report), as well as much else besides. At a stroke she implicitly wrote off the "speed kills" misguided rubbish, though it has grown since driven by power, money and politics regrettably leading to alienation of our law enforcement and undermining respect for everyone involved.

http://web.archive.org/web/20040816035301/http://w...

So my response to the question about how we should set limits is in this next post so that anyone quoting this post, does not have to include that one, which I imagine no one will wish to quote - if PH accepts it for size.

and finally:

"As a believer in scientific methods, as was the 1966 Congress, we as a Nation would be best served by entrusting this responsibility solely to licensed traffic engineering professionals and their institutions." I agree.

See next two posts, 517 characters short of fitting in one.

Before anyone loses the will to live seeing the length, the further into it you get, the more interesting and relevant it becomes.
Note also the comment that bad learning has gone on so long that even our engineers need to "remember" the right ways, as a profession.

Edited by anthonym on Tuesday 25th August 23:04