20mph limits..useful by schools or spawn of Satan?
Discussion
Reading the Daily Excess today (although not proud of it), in the motoring section theres a piece on 20mph limits, and how we're going to have so many more of them. Apparently a recent survey by Green Flag of its customers has shown 72 per cent are in favour of more! There is also apparently a group of backbench MP's putting pressure on the government to allow councils to put them whereever they like.
Statistical b
s used to justify them: 69 per cent of people break 30mph limits (because they are often to low...so lets make them lower!...criminal fcuking genius at work or what?)
40 per cent of pedestrians struck at 20mph or less suffer serious injury compared to 90 per cent struck at 30mph plus. (This argument has always struck me as completely false; this presumes most accidents occur with no braking prior to impact, which I doubt. I would love to see figures comparing actual impact speed to the travelling speed prior to any problem being observed).
I personally find 20mph limits intolerable, feels like I'm going backwards, and therefore my concentration plummets as it feels like there is no need to concentrate. What does everyone else think?
Statistical b
s used to justify them: 69 per cent of people break 30mph limits (because they are often to low...so lets make them lower!...criminal fcuking genius at work or what?) 40 per cent of pedestrians struck at 20mph or less suffer serious injury compared to 90 per cent struck at 30mph plus. (This argument has always struck me as completely false; this presumes most accidents occur with no braking prior to impact, which I doubt. I would love to see figures comparing actual impact speed to the travelling speed prior to any problem being observed).
I personally find 20mph limits intolerable, feels like I'm going backwards, and therefore my concentration plummets as it feels like there is no need to concentrate. What does everyone else think?
20 limits certainly have their place around schools AT CERTAIN TIMES - but if the school run mums parked their people-carriers and 4x4s safely there wouldn't be a problem!
I used to live in the modern estate of Lower Earley in Reading which has a few 20 limits carefully placed on through routes with humps, then the cul-de-sacs off them are 30 limits!!!
In my opinion the beaurocrats who blight our lives should certainly not be responsible for such implementations. I'd rather see a responsible mix of people such as BiB and road user groups placing them.
Assocation of British drivers has a great piece on this: www.abd.org.uk/mph20con.htm
I used to live in the modern estate of Lower Earley in Reading which has a few 20 limits carefully placed on through routes with humps, then the cul-de-sacs off them are 30 limits!!!
In my opinion the beaurocrats who blight our lives should certainly not be responsible for such implementations. I'd rather see a responsible mix of people such as BiB and road user groups placing them.
Assocation of British drivers has a great piece on this: www.abd.org.uk/mph20con.htm
Although the ABD are as guilty of statistical nonsense as the powers that be their 20mph article is, for the most part, very well reasoned IMHO. There are undoubtedly areas where 20mph limits are justified as there is no way to improve the safety of all road users by other means. An example would be a school on a narrow road. Parking (often inept) is an inevitability around the beginning and end of the day and it is, sadly, unlikely that all children will exhibit good road sense all of the time whoever well, or otherwise, they have been tutored. However, it seems unlikely that a 20mph limit would be an essential throughout the day, rather an enforced and well signed limit at the appropriate times of the day might result in greater compliance than a 20mph limit 24/7.
jaydee said:
However, it seems unlikely that a 20mph limit would be an essential throughout the day, rather an enforced and well signed limit at the appropriate times of the day might result in greater compliance than a 20mph limit 24/7.
While I still need convincing about 20mph limits, this would have to be the least objectionable way to use them. I wonder why we haven't seen time dependent speed limits before, since bus lanes (and I have a time dependent no right turn near me) have been operating on this basis for years. Too difficult for the numpties to cope with I suppose.
AlexH said:
(This argument has always struck me as completely false; this presumes most accidents occur with no braking prior to impact, which I doubt. I would love to see figures comparing actual impact speed to the travelling speed prior to any problem being observed).
I strongly agree that these claims are highly misleading. See these Safe Speed pages:
www.safespeed.org.uk/killspeed.html
www.safespeed.org.uk/proof.html
www.safespeed.org.uk/thatad.html
Best regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
At risk of turning this thread into an O/T two person debate, I can answer the following:
The information relating to the likelihood of death at a given speed is principally derived from work by the Wayne State University. Cadaver research (which continues to this day) as well as Live Body Profiling (hitting people with things and finding out what happens) has been used to provide biomechanical models of the impacts that the human body can sustain. These models are then used to calibrate the sensors of crash test dummies.
What is frequently ignored (by both sides) is that the figures pertaining to injuries and deaths are derived from work on adult impacts. There is very little information on the serious injury rates in children at given speeds, principally owing to the lack of available child cadavers, but statistical surveys of injuries treated in emergent situations suggest that children are more likely to be killed at lower speeds than adults. This is likely to be as a result of force application being more likely to the torso and head of children under 10 than to the pelvis or legs in older children and adults.
safespeed website said:
But ask yourself how they found that 20% of folk were injured at 10 km/h. Did the other 80% turn up and say they were struck at 10km/h, but they were uninjured? What? All of them? Or did they crash a car into 100 medical students at 10km/h and examine the results? Probably not we guess.
Can anyone suggest any practical technique for establishing the 20% of folk receiving minor injuries at 10 km/h?
The information relating to the likelihood of death at a given speed is principally derived from work by the Wayne State University. Cadaver research (which continues to this day) as well as Live Body Profiling (hitting people with things and finding out what happens) has been used to provide biomechanical models of the impacts that the human body can sustain. These models are then used to calibrate the sensors of crash test dummies.
What is frequently ignored (by both sides) is that the figures pertaining to injuries and deaths are derived from work on adult impacts. There is very little information on the serious injury rates in children at given speeds, principally owing to the lack of available child cadavers, but statistical surveys of injuries treated in emergent situations suggest that children are more likely to be killed at lower speeds than adults. This is likely to be as a result of force application being more likely to the torso and head of children under 10 than to the pelvis or legs in older children and adults.
jaydee said:
The information relating to the likelihood of death at a given speed is principally derived from work by the Wayne State University. Cadaver research (which continues to this day) as well as Live Body Profiling (hitting people with things and finding out what happens) has been used to provide biomechanical models of the impacts that the human body can sustain. These models are then used to calibrate the sensors of crash test dummies.
I fully accept that there are a range of doubts about the accuracy of the "risk at impact speed" figures.
But I submit that even if large errors were present they would not affect the vitally important conclusion that average impact speed is little influenced by free travelling speed. Road user response plays a far larger part especially when one properly considers all the near misses and successful avoidances.
The risk at impact speed figures imply a conclusion which is out of touch with reality to the extent of between 100:1 and 1,000:1.
And that's not to mention your valid point about risks to small children being greater - if a correction for this were made the error ratio gets even larger!
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
>> Edited by safespeed on Saturday 2nd August 13:32
safespeed said:
I fully accept that there are a range of doubts about the accuracy of the "risk at impact speed" figures.
The figures are likely to be accurate, but only for the 50th percentile male as this is where most figures have been derived (from the hybrid III dummy). I agree with your perception of the misuse of the information, I merely (and pedantically
) wished to point out that the details of injury likelihood are accurately (for a given, and limited value of accurate) derived from tests and not plucked out of the air. safespeed said:
But I submit that even if large errors were present they would not affect the vitally important conclusion that average impact speed is little influenced by free travelling speed. Road user response plays a far larger part especially when one properly considers all the near misses and successful avoidances.
Absolutely. Primary vehicle safety (being able to see out of the windows, brake rapidly and in a straight line, swerve to avoid impact etc.) and driver awareness and education to minimise the risk of impact to pedestrians are of far greater importance than the reduction of mean speeds. Having said which, there are areas where the rigorous inforcement of speed limits lower than those presently in force would be appropriate IMHO as inherent risk factors in the road layout might put even the most skilled driver in the position of being unable to avoid an impact.
safespeed said:
The risk at impact speed figures imply a conclusion which is out of touch with reality to the extent of between 100:1 and 1,000:1.
Hmm. More accurately, perhaps, the risk at impact figures are accurate (in that an impact at x mph results in a likelihood of death and serious injury of y %) but they have been misrepresented to give the statistically illiterate the impression that travelling at 30mph means that if someone steps out in front of you there's a 50-50 chance of them dying, whereas the reality is that there's a 50-50 chance only if you are unable to appreciate the situation and react to it as appropriate, be that by swerving, braking or signalling your presence.
206xsi 
But, this stuff matters ! It's what is being relied upon to spin lies (or at least half-truths) about 'safety' and further increase the burden on the motorist.
What safespeed and I would both contend (I think) is that the injury figures are being misrepresented. Safespeed has suggested on his site, in a somewhat tongue in cheek manner "Can anyone suggest any practical technique for establishing the 20% of folk receiving minor injuries at 10 km/h?" that these figures cannot be relied upon, which doesn't IMO, help 'the cause' as the figures are supportable, what is not supportable is the interpretation thereof.
:illgetmycoatandmypebblyglasses:
>> Edited by jaydee on Saturday 2nd August 13:58
But, this stuff matters ! It's what is being relied upon to spin lies (or at least half-truths) about 'safety' and further increase the burden on the motorist.
What safespeed and I would both contend (I think) is that the injury figures are being misrepresented. Safespeed has suggested on his site, in a somewhat tongue in cheek manner "Can anyone suggest any practical technique for establishing the 20% of folk receiving minor injuries at 10 km/h?" that these figures cannot be relied upon, which doesn't IMO, help 'the cause' as the figures are supportable, what is not supportable is the interpretation thereof.
:illgetmycoatandmypebblyglasses: >> Edited by jaydee on Saturday 2nd August 13:58
jaydee said:
The risk at impact speed figures imply a conclusion which is out of touch with reality to the extent of between 100:1 and 1,000:1.
Hmm. More accurately, perhaps, the risk at impact figures are accurate (in that an impact at x mph results in a likelihood of death and serious injury of y %) but they have been misrepresented to give the statistically illiterate the impression that travelling at 30mph means that if someone steps out in front of you there's a 50-50 chance of them dying, whereas the reality is that there's a 50-50 chance only if you are unable to appreciate the situation and react to it as appropriate, be that by swerving, braking or signalling your presence.
I see we're in general agreement, but a couple of details remain. In this last comment of yours, an even larger factor which you didn't mention is that drivers slow down in areas of danger anyway. Speed enforcement tends to concentrate on areas where danger is less and speeds are higher. That's just one more way in which over zealous speed enforcement misses its (supposed) road safety objectives.
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
I'd agree entirely with the contention that speed limits are currently enforced in the wrong places.
Can you state a source for this ? I know of data that drivers slow down in response to perceived risk, but this is often countered by the viewpoint that drivers, especially young and/or inexperienced drivers, are very poor at risk perception and at determining speeds that would give adequate reaction times in response to that risk they do perceive.
safespeed said:
an even larger factor which you didn't mention is that drivers slow down in areas of danger anyway.
Can you state a source for this ? I know of data that drivers slow down in response to perceived risk, but this is often countered by the viewpoint that drivers, especially young and/or inexperienced drivers, are very poor at risk perception and at determining speeds that would give adequate reaction times in response to that risk they do perceive.
jaydee said:
I'd agree entirely with the contention that speed limits are currently enforced in the wrong places.
safespeed said:
an even larger factor which you didn't mention is that drivers slow down in areas of danger anyway.
Can you state a source for this ? I know of data that drivers slow down in response to perceived risk, but this is often countered by the viewpoint that drivers, especially young and/or inexperienced drivers, are very poor at risk perception and at determining speeds that would give adequate reaction times in response to that risk they do perceive.
Well, of course to a large extent it is self evident that drivers exhibt "safe speed behaviour" or they would crash the first time they encountered stationary traffic! Then it's obvious that a half decent driver will slow dramatically if he sees kids spilling off the pavement ahead. But there's some non-explicit information in the DfT publication "VSGB" about how they have to carry out their surveys to avoid the "errors" casued by drivers slowing near hazards. I'm damned if I can find VSGB at present as the DfT have totally ruined their web site. (I just hope the objective wasn't to change history, newspeak style)
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
jaydee said:
Safespeed has suggested on his site, in a somewhat tongue in cheek manner "Can anyone suggest any practical technique for establishing the 20% of folk receiving minor injuries at 10 km/h?" that these figures cannot be relied upon, which doesn't IMO, help 'the cause' as the figures are supportable, what is not supportable is the interpretation thereof.
That quote of course, is very much an aside... A little lower on the page it says:
"We do not doubt the claim of the proportions of deaths at various impact speeds. We do not doubt the casualty figures.
What do have to take issue with is the implied relationship between vehicle speeds and pedestrian impact speeds."
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
Indeed. However, you did solicit info. on how the figures were derived in a manner that could be seen as doubting their veracity, not, IMHO, the weak spot in the argument of the powers that be.
It may be evident that some drivers respond safely to risks most of the time and most drivers respond safely to risks some of the time but there has been a view in the 'self-regulation' (for want of a better term) lobby that allowing drivers to choose their own limits is a positive move. I would argue that this is highly contentious, given the propensity for, mainly but not exclusively, younger male drivers to have a highly optimistic perception of their abilities and gravely underestimate risk.
>> Edited by jaydee on Saturday 2nd August 15:15
safespeed said:
Well, of course to a large extent it is self evident that drivers exhibt "safe speed behaviour" or they would crash the first time they encountered stationary traffic! Then it's obvious that a half decent driver will slow dramatically if he sees kids spilling off the pavement ahead.
It may be evident that some drivers respond safely to risks most of the time and most drivers respond safely to risks some of the time but there has been a view in the 'self-regulation' (for want of a better term) lobby that allowing drivers to choose their own limits is a positive move. I would argue that this is highly contentious, given the propensity for, mainly but not exclusively, younger male drivers to have a highly optimistic perception of their abilities and gravely underestimate risk.
>> Edited by jaydee on Saturday 2nd August 15:15
jaydee said:
It may be evident that some drivers respond safely to risks most of the time and most drivers respond safely to risks some of the time but there has been a view in the 'self-regulation' (for want of a better term) lobby that allowing drivers to choose their own limits is a positive move. I would argue that this is highly contentious, given the propensity for, mainly but not exclusively, younger male drivers to have a highly optimistic perception of their abilities and gravely underestimate risk.
Which clearly indicates the need to address failures in risk assessment by young men head on and not by the useless proxy of speed limit enforcement. In fact figures from Wales indicate the abject failure of the approach. See:
www.safespeed.org.uk/wrong.html
Best regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
I'll back that up with my own experiences - as an 18 year old I kept rigidly to the speed limits, but had my only ever accident (skidded off road on a dangerous bend - due completely to inexperience and a little excess speed, but was 30 UNDER the limit).
Now as a 29 year old I drive faster, but my experience can help me see upcoming dangers and my car is far better equipped to deal with them. I hope that 7 years no claims and 0 points confirms that!
Now as a 29 year old I drive faster, but my experience can help me see upcoming dangers and my car is far better equipped to deal with them. I hope that 7 years no claims and 0 points confirms that!
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