TfL Vision Zero: Lower Speed Limits

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Micro The Maniac
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Re: TfL Vision Zero: Lower Speed Limits

Post by Micro The Maniac »

Chris Bertram wrote: Tue Oct 19, 2021 18:05 It's also all too easy to "read" a speed limit roundel on the back of a van or lorry, or one in an adjacent distributor road with a lower limit, or a badly-placed sign at the entry of a side road (all these have happened to me). There will have to be a lot, and I really mean a lot, of tidying up of signage before automatic SLR can be implemented.
Don't forget signs buried in hedges...
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Re: TfL Vision Zero: Lower Speed Limits

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Bryn666 wrote: Tue Oct 19, 2021 21:01
2 Sheds wrote: Tue Oct 19, 2021 20:29
Bryn666 wrote: Tue Oct 19, 2021 20:14

They will be run using GPS data collected from speed limit orders on file. The idea of a vehicle reading a sign and panic braking on your behalf is just daft.
That makes sense, but it’s not what the press said when the proposal was announced.
When have the British press ever had anything useful to say about transport policy? It's not workable, so get people in a foamy rage about something that won't happen to sell papers...
Good point. I see you're right and it will be GPS based (that'll help get cars ready for road pricing).

From July 2022 the system will need to be fitted to newly launched models, not existing models. Pushing the accelerator to the floor will override it. And it's an EU requirement so potentially might not be fitted to all UK right hand drive models (depending on what our government decides)?
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Re: TfL Vision Zero: Lower Speed Limits

Post by Helvellyn »

2 Sheds wrote: Tue Oct 19, 2021 20:29
Bryn666 wrote: Tue Oct 19, 2021 20:14
2 Sheds wrote: Tue Oct 19, 2021 17:24
Yesterday I went to my local tip. After I left, I noticed my dash display (which reads speed limit signs) told me I was in a 5mph limit. This remained the case for a mile or two until another limit sign was picked up by the on board system. Similarly my car usually ‘thinks’ the limit is 15mph on the M1 after I’ve visited Leicester Forest Services.

It’s my understanding that these automatic limiters will be driven by on board sign reading cameras. If so they’re doomed to fail and we’ll all have to disable them from the outset.
They will be run using GPS data collected from speed limit orders on file. The idea of a vehicle reading a sign and panic braking on your behalf is just daft.
That makes sense, but it’s not what the press said when the proposal was announced.
It's a bloody obnoxious idea however it's done.
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Re: TfL Vision Zero: Lower Speed Limits

Post by trickstat »

Bryn666 wrote: Tue Oct 19, 2021 20:14
2 Sheds wrote: Tue Oct 19, 2021 17:24
jnty wrote: Fri Oct 01, 2021 12:19

Do any cars have the automatic speed limiting system that is allegedly going to become mandatory soon? Does anyone know of any evidence that is is changing behaviour? Presumably it could usher in a total step change in driver (or really car) behaviour.
Yesterday I went to my local tip. After I left, I noticed my dash display (which reads speed limit signs) told me I was in a 5mph limit. This remained the case for a mile or two until another limit sign was picked up by the on board system. Similarly my car usually ‘thinks’ the limit is 15mph on the M1 after I’ve visited Leicester Forest Services.

It’s my understanding that these automatic limiters will be driven by on board sign reading cameras. If so they’re doomed to fail and we’ll all have to disable them from the outset.
They will be run using GPS data collected from speed limit orders on file. The idea of a vehicle reading a sign and panic braking on your behalf is just daft.
Also risky if the car behind it does not have the same technology (and also perhaps less effective brakes). We all know that ideally everyone should be keeping a safe distance but we know many people don't even if they aren't actually tailgating.
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Re: TfL Vision Zero: Lower Speed Limits

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trickstat wrote: Wed Oct 20, 2021 11:04 Also risky if the car behind it does not have the same technology (and also perhaps less effective brakes). We all know that ideally everyone should be keeping a safe distance but we know many people don't even if they aren't actually tailgating.
Exactly, the Solomon Curve will come into play. Many speed limits are so far from the make that a single car going the limit will cause traffic to bunch together increasing accident risks. At least in Bristol most arterial roads were saved from the 20 limits although there is the issue of extreme level of non-uniformity or limits that change in seemingly arbitrary places.
However in Cardiff someone appears to have gone "f*** it" and paid no attention to differing road standards etc to the extent that even some 20mph campaigners have been irked by the inclusion of some of them.
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Re: TfL Vision Zero: Lower Speed Limits

Post by Glenn A »

Pro car I might be, but I couldn't think of anything worse than driving and trying to park in inner London, and there are better alternatives to get from Streatham to the city centre than the A23. Obviously driving in the suburbs makes more sense, where there are more shopping centres and workplaces with parking, but the congestion charge, eye watering parking charges if you can get parked and aggressive parking enforcement are a complete deterrent in inner London.
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Re: TfL Vision Zero: Lower Speed Limits

Post by RichardA35 »

ajuk wrote: Sun Nov 07, 2021 02:33
trickstat wrote: Wed Oct 20, 2021 11:04 Also risky if the car behind it does not have the same technology (and also perhaps less effective brakes). We all know that ideally everyone should be keeping a safe distance but we know many people don't even if they aren't actually tailgating.
Exactly, the Solomon Curve will come into play. Many speed limits are so far from the make that a single car going the limit will cause traffic to bunch together increasing accident risks. At least in Bristol most arterial roads were saved from the 20 limits although there is the issue of extreme level of non-uniformity or limits that change in seemingly arbitrary places.
However in Cardiff someone appears to have gone "f*** it" and paid no attention to differing road standards etc to the extent that even some 20mph campaigners have been irked by the inclusion of some of them.
If I recall the original study was on US freeways at higher speeds. Can you point me to some relevant research/evidence that makes this applicable for UK urban areas at a speed of 20mph? Thanks.
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Re: TfL Vision Zero: Lower Speed Limits

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RichardA35 wrote: Sun Nov 07, 2021 19:24
ajuk wrote: Sun Nov 07, 2021 02:33
trickstat wrote: Wed Oct 20, 2021 11:04 Also risky if the car behind it does not have the same technology (and also perhaps less effective brakes). We all know that ideally everyone should be keeping a safe distance but we know many people don't even if they aren't actually tailgating.
Exactly, the Solomon Curve will come into play. Many speed limits are so far from the make that a single car going the limit will cause traffic to bunch together increasing accident risks. At least in Bristol most arterial roads were saved from the 20 limits although there is the issue of extreme level of non-uniformity or limits that change in seemingly arbitrary places.
However in Cardiff someone appears to have gone "f*** it" and paid no attention to differing road standards etc to the extent that even some 20mph campaigners have been irked by the inclusion of some of them.
If I recall the original study was on US freeways at higher speeds. Can you point me to some relevant research/evidence that makes this applicable for UK urban areas at a speed of 20mph? Thanks.
I'm not sure I can, but you're intuition should tell you why driving significantly slower than the mean traffic flow increases your accident risk. I know the DVSA think so, driving too slow (providing it's clearly safe to go faster) is a major fault on the driving test, my Step-Dad's failed people for it before, obviously if the speed limit overrides this but he tries to avoid some of the more unrealistic 20 limits when testing people. He's also told me he's let people off for slightly exceeding a 20mph speed limit and given them a minor, conversely he's failed people for driving too fast even though that was under the posted speed limit.

The idea should be you can drive safe if your speedo was broken. In Bristol, every main road they looked at had non-compliance of over 90%, so I'm not sure how the speed limit is meant to single out or target those most likely to do harm.
I get exasperated with people who will, for all intents, argue to prohibit their own normal driving behaviour. If you didn't think you were driving safe in the first place, you shouldn't have been driving in the first place.
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Re: TfL Vision Zero: Lower Speed Limits

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ajuk wrote: Mon Nov 08, 2021 01:37 If you didn't think you were driving safe in the first place, you shouldn't have been driving in the first place.
Erm, most people who walk away from a serious collision and then end up in court argue their driving was safe... it's always the other person's fault, how could I be expected to know a child might run out in front of me despite being in a massive urban area where children are likely to be present, etc, etc.

So no, this is a nonsense argument, drivers generally are very poor arbiters of what constitutes safety given the antics I witness on a daily basis.
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Re: TfL Vision Zero: Lower Speed Limits

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ajuk wrote: Mon Nov 08, 2021 01:37
RichardA35 wrote: Sun Nov 07, 2021 19:24
ajuk wrote: Sun Nov 07, 2021 02:33

Exactly, the Solomon Curve will come into play. Many speed limits are so far from the make that a single car going the limit will cause traffic to bunch together increasing accident risks. At least in Bristol most arterial roads were saved from the 20 limits although there is the issue of extreme level of non-uniformity or limits that change in seemingly arbitrary places.
However in Cardiff someone appears to have gone "f*** it" and paid no attention to differing road standards etc to the extent that even some 20mph campaigners have been irked by the inclusion of some of them.
If I recall the original study was on US freeways at higher speeds. Can you point me to some relevant research/evidence that makes this applicable for UK urban areas at a speed of 20mph? Thanks.
I'm not sure I can, but you're intuition should tell you why driving significantly slower than the mean traffic flow increases your accident risk....
My intuition tells me that people who cannot provide evidence or a study to back up their statements should be taken with a pinch of salt. Often the conclusion of properly performed studies are counter to intuition - e.g. the principle of slowing down traffic from 70mph on controlled motorways to reduce gaps and smooth out flow.
How does a study on a freeway where pedestrians and cyclists are excluded give any comparison to a 20mph zone where these modes are present and traffic speeds will be an average across a broader range of modes? What weight is given to risks from the different modes present etc.
Not everything is to do with car travel.
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Re: TfL Vision Zero: Lower Speed Limits

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Bryn666 wrote: Mon Nov 08, 2021 10:04
ajuk wrote: Mon Nov 08, 2021 01:37 If you didn't think you were driving safe in the first place, you shouldn't have been driving in the first place.
Erm, most people who walk away from a serious collision and then end up in court argue their driving was safe... it's always the other person's fault, how could I be expected to know a child might run out in front of me despite being in a massive urban area where children are likely to be present, etc, etc.

So no, this is a nonsense argument, drivers generally are very poor arbiters of what constitutes safety given the antics I witness on a daily basis.
Don't give them a licence then. I think I've said before but when I was assessing van drivers at ASDA, what I wanted to do was cover up their speedos.
We're back to drivers can't be trusted, so stick some signs up again. A negative feedback loop is a zero sum game.
I see that on a daily basis as well, and wonder why people think the solution is to prohibit the behaviour of more sensible drivers in the hope the faster drivers will only dare go X amount over the posted limit.
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Re: TfL Vision Zero: Lower Speed Limits

Post by Bryn666 »

ajuk wrote: Mon Nov 08, 2021 12:40
Bryn666 wrote: Mon Nov 08, 2021 10:04
ajuk wrote: Mon Nov 08, 2021 01:37 If you didn't think you were driving safe in the first place, you shouldn't have been driving in the first place.
Erm, most people who walk away from a serious collision and then end up in court argue their driving was safe... it's always the other person's fault, how could I be expected to know a child might run out in front of me despite being in a massive urban area where children are likely to be present, etc, etc.

So no, this is a nonsense argument, drivers generally are very poor arbiters of what constitutes safety given the antics I witness on a daily basis.
Don't give them a licence then. I think I've said before but when I was assessing van drivers at ASDA, what I wanted to do was cover up their speedos.
We're back to drivers can't be trusted, so stick some signs up again. A negative feedback loop is a zero sum game.
I see that on a daily basis as well, and wonder why people think the solution is to prohibit the behaviour of more sensible drivers in the hope the faster drivers will only dare go X amount over the posted limit.
If you've been paying attention you will note that I have been arguing for mandatory retesting of drivers every 5 years and 'continued professional development' style training courses to be offered to ensure that anyone holding a driving licence is fit and competent to use the highways. Apparently doing stuff like this is evil though, because too many drivers are entitled and feel victimised by being asked to make sure they're not going to kill anyone.
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Re: TfL Vision Zero: Lower Speed Limits

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AJUK wrote: Mon Nov 08, 2021 10:57 I'm not sure I can, but you're intuition should tell you why driving significantly slower than the mean traffic flow increases your accident risk....
My intuition tells me that people who cannot provide evidence or a study to back up their statements should be taken with a pinch of salt.
A quick Google got me this. Often the risk may not be from speed itself, but the expectation of lower speeds as a result of the councils setting speed limits significantly below what the road was designed for, however there is evidence to suggest setting speed limits slightly below engineering recommendations may reduce accidents.
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Re: TfL Vision Zero: Lower Speed Limits

Post by RichardA35 »

ajuk wrote: Mon Nov 08, 2021 12:57
AJUK wrote: Mon Nov 08, 2021 10:57 I'm not sure I can, but you're intuition should tell you why driving significantly slower than the mean traffic flow increases your accident risk....
My intuition tells me that people who cannot provide evidence or a study to back up their statements should be taken with a pinch of salt.
A quick Google got me this. Often the risk may not be from speed itself, but the expectation of lower speeds as a result of the councils setting speed limits significantly below what the road was designed for, however there is evidence to suggest setting speed limits slightly below engineering recommendations may reduce accidents.
A quick read of the abstracts:
1st ref:..."Ill-judged overtaking, tailbacks sparking road-rage, and those who fail to merge properly with motorways"...
so not an urban 20mph context
2nd ref:... "The researchers found that vehicles were two times more likely to obey the speed limit at locations with higher posted speed limits set at 50 mph or 55 mph compared to the base case of less than 50 mph, and four times more likely to obey when the posted speed limit was between 60 and 70 mph."
A Montana based study not related to UK 20mph limits
I'm nowhere near competent to judge on these things and I recognise this despite having been working in the construction industry for more years than I remember, so to convince anyone with a bit of competence will take a step change from what has been presented so far.
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Re: TfL Vision Zero: Lower Speed Limits

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ajuk wrote: Mon Nov 08, 2021 01:37 you're intuition should tell you...
In the past, safety-critical workers like pilots and surgeons used to think they could operate on raw skill and intuition alone; that any procedures or equipment which restricted or controlled them was almost certainly going to make things worse. It was of course nonsense - evidence has shown that the introduction of fixed checklists, procedures and equipment which account for many common human fallibilities has saved lives and vastly reduced the number of accidental deaths across the board.

Yet in motoring, we still cling to the notion that intuition is king - that drivers are able to judge hundreds of different environmental factors on an ongoing and select a 'safe' speed for every circumstance. The notion that 'the road must fit the speed limit' is a laudable goal and perhaps in the past was the only practical method of widespread enforcement, but it removes responsibility from the driver for rationally controlling their own sense of instinctive frustration and pretends that the only factor determining appropriate speed are hazards that the driver can see. It also assumes that we have a blank chequebook to continually adjust the design of streets all over the country!

The fact that technology gives us an increasing number of ways to cheaply control traffic speeds without needing to beg drivers via signage or environmental cues should be lauded; history has shown that the less you rely on human judgement when performing safety critical tasks, the safer they become.
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Re: TfL Vision Zero: Lower Speed Limits

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ajuk wrote: Mon Nov 08, 2021 01:37 I get exasperated with people who will, for all intents, argue to prohibit their own normal driving behaviour. If you didn't think you were driving safe in the first place, you shouldn't have been driving in the first place.
That seems to apply to a remarkably large number of drivers, I have had two cars written off by drivers who drove into the back of me when I was in a stationary queue in an urban area in daylight. The last one not only wrote off my car but the vehicle in front of me. This is where it happened - in a 30 mph area on a saturday afternoon.

https://www.google.co.uk/maps/@51.58357 ... 8192?hl=en

the police reckoned the car was doing at least 45 mph when it hit me. I had been waiting for several seconds before this happened. The other driver gave as an excuse that if I hadnt stopped, for the red light on the pedestrian crossing it would never have happened. It also turned out that he had no insurance of driving license so to add to the fun I lost my NCB. Very few people who screw things up badly enough to get into such mess will agree their driving was substandard it will be rationalised as the fault of the person who's vehicle they collided with.
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Re: TfL Vision Zero: Lower Speed Limits

Post by fras »

KeithW wrote: Mon Nov 08, 2021 17:52
ajuk wrote: Mon Nov 08, 2021 01:37 I get exasperated with people who will, for all intents, argue to prohibit their own normal driving behaviour. If you didn't think you were driving safe in the first place, you shouldn't have been driving in the first place.
That seems to apply to a remarkably large number of drivers, I have had two cars written off by drivers who drove into the back of me when I was in a stationary queue in an urban area in daylight. The last one not only wrote off my car but the vehicle in front of me. This is where it happened - in a 30 mph area on a saturday afternoon.

https://www.google.co.uk/maps/@51.58357 ... 8192?hl=en

the police reckoned the car was doing at least 45 mph when it hit me. I had been waiting for several seconds before this happened. The other driver gave as an excuse that if I hadnt stopped, for the red light on the pedestrian crossing it would never have happened. It also turned out that he had no insurance of driving license so to add to the fun I lost my NCB. Very few people who screw things up badly enough to get into such mess will agree their driving was substandard it will be rationalised as the fault of the person who's vehicle they collided with.
Surely the issue here is that we allow dangerous drivers onto our roads, as the penalties are so ridiculously low compared to those for "normal" criminality. The standards of some people's driving is so low one wonders how they manage to get through a single week without writing the car off !
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Re: TfL Vision Zero: Lower Speed Limits

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jnty wrote: Mon Nov 08, 2021 14:06
ajuk wrote: Mon Nov 08, 2021 01:37 you're intuition should tell you...
In the past, safety-critical workers like pilots and surgeons used to think they could operate on raw skill and intuition alone; that any procedures or equipment which restricted or controlled them was almost certainly going to make things worse. It was of course nonsense - evidence has shown that the introduction of fixed checklists, procedures and equipment which account for many common human fallibilities has saved lives and vastly reduced the number of accidental deaths across the board.

Yet in motoring, we still cling to the notion that intuition is king - that drivers are able to judge hundreds of different environmental factors on an ongoing and select a 'safe' speed for every circumstance. The notion that 'the road must fit the speed limit' is a laudable goal and perhaps in the past was the only practical method of widespread enforcement, but it removes responsibility from the driver for rationally controlling their own sense of instinctive frustration and pretends that the only factor determining appropriate speed are hazards that the driver can see. It also assumes that we have a blank chequebook to continually adjust the design of streets all over the country!

The fact that technology gives us an increasing number of ways to cheaply control traffic speeds without needing to beg drivers via signage or environmental cues should be lauded; history has shown that the less you rely on human judgement when performing safety critical tasks, the safer they become.
Yes, most people have a strong aversion to having crashes, or running people over, that's why (and contrary to very popular opinion) more reasonable speed limits just tend to have higher levels of speed limit compliance, but not higher speeds. Most ordinary tight residential streets like this do have average speeds well below 30, even when they technically had a 30 limit. Obviously going 30 or even close to it is never sensible down streets like that, but that's why it's good that UK limits are set by street lights rather than signs designed to encourage a "safe speed".
That said my opposition to 20 limits is more about when they put them on roads like this, especially when there are so many other roads in the city of a lower standard that retained their 30 limits. 🤦‍♂️
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Re: TfL Vision Zero: Lower Speed Limits

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ajuk wrote: Mon Nov 08, 2021 21:16 Yes, most people have a strong aversion to having crashes, or running people over, that's why (and contrary to very popular opinion) more reasonable speed limits just tend to have higher levels of speed limit compliance, but not higher speeds. Most ordinary tight residential streets like this do have average speeds well below 30, even when they technically had a 30 limit. Obviously going 30 or even close to it is never sensible down streets like that, but that's why it's good that UK limits are set by street lights rather than signs designed to encourage a "safe speed".
That said my opposition to 20 limits is more about when they put them on roads like this, especially when there are so many other roads in the city of a lower standard that retained their 30 limits. 🤦‍♂️
People generally don't want to crash or run people over yet we have no intuitive ways of actually trading off the risks involved. Even if drivers were constantly furnished with the full risk profile of a given road (which they could never possibly be) there's no set 'acceptable risk' which all drivers drive to - it's just driven off intuition based on what everyone else does.

If humans genuinely had an aversion to killing pedestrians and drove to this, rather than the limit, we'd never ever drive at 40mph or above in any remotely populated area, because at that speed hitting a pedestrian who unwittingly steps out would be almost certainly fatal. Yet we do - so we're obviously accepting some level of risk on the behalf of others. Are we really capable of intuitively understanding or trading off this risk - could we express, in rough numerical terms perhaps, what risk factor we're driving to (and what might be unacceptable?) Or are we just thinking 'big road, drive fast, nothing bad happened yesterday'?
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Re: TfL Vision Zero: Lower Speed Limits

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jnty wrote: Tue Nov 09, 2021 10:40
ajuk wrote: Mon Nov 08, 2021 21:16 Yes, most people have a strong aversion to having crashes, or running people over, that's why (and contrary to very popular opinion) more reasonable speed limits just tend to have higher levels of speed limit compliance, but not higher speeds. Most ordinary tight residential streets like this do have average speeds well below 30, even when they technically had a 30 limit. Obviously going 30 or even close to it is never sensible down streets like that, but that's why it's good that UK limits are set by street lights rather than signs designed to encourage a "safe speed".
That said my opposition to 20 limits is more about when they put them on roads like this, especially when there are so many other roads in the city of a lower standard that retained their 30 limits. 🤦‍♂️
People generally don't want to crash or run people over yet we have no intuitive ways of actually trading off the risks involved. Even if drivers were constantly furnished with the full risk profile of a given road (which they could never possibly be) there's no set 'acceptable risk' which all drivers drive to - it's just driven off intuition based on what everyone else does.

If humans genuinely had an aversion to killing pedestrians and drove to this, rather than the limit, we'd never ever drive at 40mph or above in any remotely populated area, because at that speed hitting a pedestrian who unwittingly steps out would be almost certainly fatal. Yet we do - so we're obviously accepting some level of risk on the behalf of others. Are we really capable of intuitively understanding or trading off this risk - could we express, in rough numerical terms perhaps, what risk factor we're driving to (and what might be unacceptable?) Or are we just thinking 'big road, drive fast, nothing bad happened yesterday'?
That's just it, they don't just drive to the limit. TBH that's also what I also assumed was the case, but if you look at data from hidden radar detection, that shows the sheer level to which road design dictates traffic speeds.
Heron Way in Chipping Sodbury has a 40 limit, it has repeaters on it just to remind people that they can go 40 and yet the average speed was 31 and 85th percentile speeds was 36,both lower than several roads in the same urban area with 30 limit, one 30 limit road had an average speed of 38! I think the level of compliance was just over 91%, but that was the level taken from the fastest of the 3 data points.
This is the sort of data that showed me the discrepancy between limits and actual speeds that I can't un-see. First time I've ever laughed at a FOI request result.

Urban 40 limits are some of the most obeyed speed limits in the UK, and yes hitting someone actually at 40 is likely death, but that's the reason why you have the limit there in the first place. Raising the speed limit on a road to 40 does very little to increase average speeds if they do at all and may even cause them to drop slightly.
They're there more to warn pedestrians of the increase road danger. South Gloucestershire have been removing most urban 40 limits despite me finding data that showed many of the higher standard 30 limit roads actually had higher average and 85th percentile speeds than other roads in the same urban area with 40 limits. I think they're just perfectly happy to mislead people.
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