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 » Sat Sep 18, 2021 09:13

ajuk wrote:
Sat Sep 18, 2021 00:36
You seem to be alluding to the hypothesis that if you set the speed limit lower than many or most drivers will only only drive X amount over or under the posted limit.
I have to admit I used to assume that to be true, but it's not by a long chalk. That claim has come to be like nails down a chalk board to me, so I wrote a blog post about it.
I'm sure I've mentioned elsewhere the case study of a rural road near me... it was a self policing national speed limit road - self policing in that it twists and turns across the heathland. It is mostly perfectly driveable at approaching 60mph, slowing as needed for the bends. Unfortunately two cars, in quick succession, failed to take one of the bends, hitting the same sturdy tree... six teenagers were killed.

It should be noted that in both cases, the estimated impact speed was in excess of 100mph... at night, in the wet. And alcohol was a factor.
The idea is; some people are breaking the law, and the solution is to criminalise the behaviour of people not breaking that law, in order to stop people breaking that law.
The immediate cry of "something must be done" has resulted in the road getting a 30mph limit, with regular policing when it was still high in people's memory. Quite a few people were been done for 33.

It should also be noted that, with most cars obeying the limit, the numpty (sorry!) drivers still drive like idiots (sorry!).

As an aside, the 30 limit is now mostly treated with the contempt it deserves by most drivers... and the local plod have better things to do than sit on a country road with low traffic levels. They are dealing with the more populist issues, like guarding protesters.

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Re: TfL Vision Zero: Lower Speed Limits

Post by 2 Sheds » Sat Sep 18, 2021 10:53

Debaser wrote:
Sat Sep 18, 2021 09:06
2 Sheds wrote:
Thu Sep 16, 2021 14:24
Bryn666 wrote:
Sun Sep 12, 2021 16:00
You provide safe cycling infrastructure, places to store bikes, etc.

Something like 15% of all city land is given over to car parking. Imagine what we could do with that if we were more creative - and yes, some of that land could be multi storey or underground with human priority facilities on top like houses and shops.
I’m interested to see your source for this. Not any city I know.
This study refers to London - 16% of its streets given over to parking. Other international studies appear to be available.
Ah, interesting. Percentage of streets differs somewhat from percentage of land. This amounts to about 5 % then.

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Re: TfL Vision Zero: Lower Speed Limits

Post by pjr10th » Sat Sep 18, 2021 21:58

ajuk wrote:
Sat Sep 18, 2021 00:36
pjr10th wrote:
Fri Sep 17, 2021 16:09
ajuk wrote:
Fri Sep 17, 2021 14:50
Trying to get more drivers to drive more sensible speeds is not exactly a new idea, if just setting the speed limit really low was thought to work, that would always have been the way you set them.
What I think is quite insidious is when councils drop speed limits knowing in advance of doing it that even if their most optimistic expectation for an average speed drop is met, the average speed will still be well over the speed limit, so it's non-compliance by design.

As someone people may have pointed out in already in this thread, by including higher-standard and main roads in 20 schemes it may only serve to water down any effect a 20 limit might have on ordinary tight residential streets and sat-navs may no longer see those main roads as faster and send more cars down ordinary residential streets.
Modern sat navs are normally good enough to not bother with speed limits, but the actual speeds of the vehicles. The only way to stop motor vehicles rat running down side streets is to physically or legally prevent them from doing so. Not to mention local drivers as well.

When these speed limits are set, they should be set with a view to doing the engineering work when possible within highway authorities' funds. However, it's better to have a 20mph limit on a badly designed residential road than a 30mph limit because then at least local residents & good drivers will help to bring down speeds somewhat. If you set it at 30mph, then barely anyone will go under 30mph, provided the road is clear. If you set it at 20mph, then at least you will get some drivers doing 20mph and the police will have the powers to enforce safe speeds if they want to.
I can only say is I've come across this in a few part of Bristol. I know SatNavs often look at average speeds, but if the limit is lower than the average speed then it goes by the limit rather than working on the assumption most people will exceed the limit.

You seem to be alluding to the hypothesis that if you set the speed limit lower than many or most drivers will only only drive X amount over or under the posted limit.
I have to admit I used to assume that to be true, but it's not by a long chalk. That claim has come to be like nails down a chalk board to me, so I wrote a blog post about it.
You may achieve a very small average speed drop of about 1mph, but it's the fastest drivers who are least likely to slow down, most likely to do harm and they're also the one properly set speed limits are more efficient at targeting.
My point isn't that a lower signed speed limit will magically immediately lower the speed of all drivers. My point is that the average driver has a tendency to slightly overspeed but not a tendency to underspeed. If you have a 30mph speed limit, near to noone will travel at 20mph if the road is clear ahead. In fact you'll get a fair few who will travel at 40mph+, while if you have a 20mph limit, you will get some drivers who will sit at 20mph, especially if it's enforced.

The key point should be national consistency, so drivers know what speed limit to expect for the road they're on. And 20mph should be the appropriate limit on the majority of urban & village streets, with the exception of the main motorist roads on your network (main roads which also don't have high place value, such as shopping streets or streets in the city/town centre). 40mph should only be used where frontal development is limited and there are low numbers of pedestrians and cyclists, e.g. the London North Circular (but even some of that should be 30).

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Re: TfL Vision Zero: Lower Speed Limits

Post by ajuk » Sun Sep 19, 2021 01:50

Micro The Maniac wrote:
Sat Sep 18, 2021 09:13
ajuk wrote:
Sat Sep 18, 2021 00:36
You seem to be alluding to the hypothesis that if you set the speed limit lower than many or most drivers will only only drive X amount over or under the posted limit.
I have to admit I used to assume that to be true, but it's not by a long chalk. That claim has come to be like nails down a chalk board to me, so I wrote a blog post about it.
I'm sure I've mentioned elsewhere the case study of a rural road near me... it was a self policing national speed limit road - self policing in that it twists and turns across the heathland. It is mostly perfectly driveable at approaching 60mph, slowing as needed for the bends. Unfortunately two cars, in quick succession, failed to take one of the bends, hitting the same sturdy tree... six teenagers were killed.

It should be noted that in both cases, the estimated impact speed was in excess of 100mph... at night, in the wet. And alcohol was a factor.
The idea is; some people are breaking the law, and the solution is to criminalise the behaviour of people not breaking that law, in order to stop people breaking that law.
The immediate cry of "something must be done" has resulted in the road getting a 30mph limit, with regular policing when it was still high in people's memory. Quite a few people were been done for 33.

It should also be noted that, with most cars obeying the limit, the numpty (sorry!) drivers still drive like idiots (sorry!).

As an aside, the 30 limit is now mostly treated with the contempt it deserves by most drivers... and the local plod have better things to do than sit on a country road with low traffic levels. They are dealing with the more populist issues, like guarding protesters.
I'm reminded of this section of this video. "If you only ticked more afternoon commuters, those stupidity induced late night teen fatalities would never have happened" :roll:

Sounds to me like that crash was already down to people driving dangerously and recklessly, that's not the people who will slow down because the limit has been made lower, they're the least likely to do so. People don't drive too fast because the speed limit lets them or because it's only slightly over the posted limit.
It sounds like the road into Cheddar, it was reduced from NSL to 30 because it's popular with drifters. They're notorious for their speed limit obedience. 🤦
Getting to over 30 down there is a mission for most people, I certainly wouldn't have argued to have a 40 limit along there, just no signs encouraging a speed, but now there's no longer a 30 limit for traffic entering Cheddar.
pjr10th wrote:
Sat Sep 18, 2021 21:58

My point isn't that a lower signed speed limit will magically immediately lower the speed of all drivers. My point is that the average driver has a tendency to slightly overspeed but not a tendency to underspeed. If you have a 30mph speed limit, near to noone will travel at 20mph if the road is clear ahead. In fact you'll get a fair few who will travel at 40mph+, while if you have a 20mph limit, you will get some drivers who will sit at 20mph, especially if it's enforced.

The key point should be national consistency, so drivers know what speed limit to expect for the road they're on. And 20mph should be the appropriate limit on the majority of urban & village streets, with the exception of the main motorist roads on your network (main roads which also don't have high place value, such as shopping streets or streets in the city/town centre). 40mph should only be used where frontal development is limited and there are low numbers of pedestrians and cyclists, e.g. the London North Circular (but even some of that should be 30).
No, that's not true, drivers overwhelmingly judge their speed by the design of the road and the conditions at the time not by speed limits.
I know of many 40 limit roads in South Gloucestershire that have lower average and 85th percentile speeds than a near by 30 limit road of a similar design.
You can have road that has a seemingly generous 40 limit lined with repeaters reminding people they can go 40 but the average speed is consistently in the low 30s and the level of compliance over 90%! Why? Because more people were parking on it the 40 limit road than on the 30 limit one and there were houses on both sides. The 40 limit do more warn pedestrians of the greater road danger, than they do to speed up traffic.
Yes, they do look to measure free-flowing average speeds for these surveys.
Yes, this sort of thing initially surprised me too.

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Re: TfL Vision Zero: Lower Speed Limits

Post by thatapanydude » Thu Sep 30, 2021 23:44

thatapanydude wrote:
Fri Sep 10, 2021 13:20
.....as I suspect there will be more on the way.
TfL are at least reviewing the Streetview changes on Park Lane and more importantly on Euston Road as well as others.

Whilst I am yet to reply to the "discussion", I do think both roads should revert to the pre-covid setup. Though the issue with Park Lane might be the royal park as they are trying to stop cyclists using Hyde Park. This stretch also might be in conjunction with what TfL decide on the extent of 20mph on Park Lane.
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Re: TfL Vision Zero: Lower Speed Limits

Post by jnty » Fri Oct 01, 2021 12:19

ajuk wrote:
Sun Sep 19, 2021 01:50
No, that's not true, drivers overwhelmingly judge their speed by the design of the road and the conditions at the time not by speed limits.
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.

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Re: TfL Vision Zero: Lower Speed Limits

Post by ajuk » Sat Oct 02, 2021 15:25

jnty wrote:
Fri Oct 01, 2021 12:19
ajuk wrote:
Sun Sep 19, 2021 01:50
No, that's not true, drivers overwhelmingly judge their speed by the design of the road and the conditions at the time not by speed limits.
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.
Probably, by forcing some people to drive significantly slower than the mean traffic flow, it may increase their accident risk.

Some of the roads in Bristol with 20 limits are of the standard that had you tried to do 20 along them during a driving exam when the limit was still 30 (and providing it was clearly safe to go faster than that under the prevailing conditions) it would have constituted a major fault, he will fail people for that. He wouldn't fail them for not going 30, but if you clearly go too slow that's a major fault, especially if cars mounted up behind you.
Conversely trying to drive 30 or even close to it down a narrow residential street lined with parked cars would also be a major fault and an instant failure.

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Re: TfL Vision Zero: Lower Speed Limits

Post by thatapanydude » Tue Oct 19, 2021 13:13

A real disappointment to say this (as a petrolhead who never got the chance to blast through before the specs in 2015 - FYI I am a young driver) but The New Civil Engineer are reporting that unfortunately the Westway will remain at 30mph on a permanent basis even after the works are completed.

As many of you will now I think it is a complete and utter disgrace in particular on the basis of the A40 being grade separated, having no cycle access etc etc - anyway the point is lost. One can only hope that a change of administration in 2024 (one with more sympathy to car users can at some point look again) !!
Last edited by thatapanydude on Tue Oct 19, 2021 16:33, edited 1 time in total.
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Re: TfL Vision Zero: Lower Speed Limits

Post by Bryn666 » Tue Oct 19, 2021 15:28

thatapanydude wrote:
Tue Oct 19, 2021 13:13
A real disappointment to say this (as a petrolhead who never got the chance to blast through before the specs in 2015) but The New Civil Engineer are reporting that unfortunately the Westway will remain at 30mph on a permanent basis even after the works are completed.

As many of you will now I think it is a complete and utter disgrace in particular on the basis of the A40 being grade separated, having no cycle access etc etc - anyway the point is lost. One can only hope that a change of administration in 2024 (one with more sympathy to car users can at some point look again) !!
40 would be fine, 30 is too low and there's no safety reason for it either.
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Re: TfL Vision Zero: Lower Speed Limits

Post by thatapanydude » Tue Oct 19, 2021 16:32

Bryn666 wrote:
Tue Oct 19, 2021 15:28

40 would be fine, 30 is too low and there's no safety reason for it either.
To have the Westway at 30mph while Hanger Lane to Savoy is at 40mph?? Just shows how TfL clearly aren't implementing cuts on the actual layout of the road rather a merely on the basis to frustrate drivers.
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Re: TfL Vision Zero: Lower Speed Limits

Post by Chris Bertram » Tue Oct 19, 2021 16:48

How is compliance with this 30 limit achieved? Are there average speed cameras? If not, do the Met Police carry out radar enforcement? Or is it widely ignored?
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Re: TfL Vision Zero: Lower Speed Limits

Post by thatapanydude » Tue Oct 19, 2021 16:59

Chris Bertram wrote:
Tue Oct 19, 2021 16:48
How is compliance with this 30 limit achieved? Are there average speed cameras?
There are average speed cameras for nearly 9 miles from Paddington to Northolt on the A40, unfortunately.

If there was no specs, I would not care as much as I doubt even the Met would enforce it, that is how slow 30mph on the Westway is.

For context the A12 section from the A11 to Hackney Wick is similar to the Westway in being D3 with a HS and while its 40mph it has one or two fixed point cameras so traffic can flow at 50mph+ which is very reasonable.
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Re: TfL Vision Zero: Lower Speed Limits

Post by Bryn666 » Tue Oct 19, 2021 17:03

thatapanydude wrote:
Tue Oct 19, 2021 16:32
Bryn666 wrote:
Tue Oct 19, 2021 15:28

40 would be fine, 30 is too low and there's no safety reason for it either.
To have the Westway at 30mph while Hanger Lane to Savoy is at 40mph?? Just shows how TfL clearly aren't implementing cuts on the actual layout of the road rather a merely on the basis to frustrate drivers.
I suspect the fear of continued damage to the structure is the reason for the 30 limit, rather than tin foil motorist victimisation. However, unless this is communicated to road users "we need to keep this at 30 or it might collapse" kind of thing, why is anyone going to actually respect its presence?

It should be 40 from Hanger Lane all the way to the start of the Paddington Flyover for sure. There are no conflicts with other classes of traffic on the Westway, but there are sufficient residential properties around to justify a noise reduction speed limit (40 makes fewer decibels than the original 60!), as well as to avoid having everything slamming into the first signals on Marylebone Road at speed.

It doesn't strike me as a particularly engineering led speed limit, at least you can work out the reason for the 20s elsewhere.
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Re: TfL Vision Zero: Lower Speed Limits

Post by 2 Sheds » Tue Oct 19, 2021 17:24

jnty wrote:
Fri Oct 01, 2021 12:19
ajuk wrote:
Sun Sep 19, 2021 01:50
No, that's not true, drivers overwhelmingly judge their speed by the design of the road and the conditions at the time not by speed limits.
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.

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Re: TfL Vision Zero: Lower Speed Limits

Post by Chris Bertram » Tue Oct 19, 2021 18:05

2 Sheds wrote:
Tue Oct 19, 2021 17:24
jnty wrote:
Fri Oct 01, 2021 12:19
ajuk wrote:
Sun Sep 19, 2021 01:50
No, that's not true, drivers overwhelmingly judge their speed by the design of the road and the conditions at the time not by speed limits.
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.
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.
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Re: TfL Vision Zero: Lower Speed Limits

Post by Big L » Tue Oct 19, 2021 19:52

Chris Bertram wrote:
Tue Oct 19, 2021 18:05
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.
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 householders that stick 20 roundels on their gateposts, wheeliebins etc. in 30 or 40 zones.
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Re: TfL Vision Zero: Lower Speed Limits

Post by Bryn666 » Tue Oct 19, 2021 20:14

2 Sheds wrote:
Tue Oct 19, 2021 17:24
jnty wrote:
Fri Oct 01, 2021 12:19
ajuk wrote:
Sun Sep 19, 2021 01:50
No, that's not true, drivers overwhelmingly judge their speed by the design of the road and the conditions at the time not by speed limits.
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.
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Re: TfL Vision Zero: Lower Speed Limits

Post by 2 Sheds » Tue Oct 19, 2021 20:29

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.
That makes sense, but it’s not what the press said when the proposal was announced.

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Re: TfL Vision Zero: Lower Speed Limits

Post by Bryn666 » Tue Oct 19, 2021 21:01

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.
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...
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Re: TfL Vision Zero: Lower Speed Limits

Post by Chris5156 » Tue Oct 19, 2021 22:41

thatapanydude wrote:
Tue Oct 19, 2021 13:13
One can only hope that a change of administration in 2024 (one with more sympathy to car users can at some point look again) !!
That’s a bit naive to the political realities. The cuts to 20mph within Westminster, whether in Westminster or TfL managed roads, are happening at the request of Westminster Council which is firmly and staunchly Tory led. If they’ve taken this line who are you hoping to see voted in?

Equally, many of TfL’s moves in terms of speed limits and changes to the road network have been happening along similar lines for the last 20 years and the furthest Bojo went when he was mayor was to pledge to “smooth the flow of traffic”, which resulted in a handful of signal installations being removed and others being retimed.

I personally disagree with the 30 limit on Westway, but realistically, raising urban speed limits is not in the manifesto of any major party in London because it’s not a vote winner.
Chris Bertram wrote:
Tue Oct 19, 2021 16:48
How is compliance with this 30 limit achieved? Are there average speed cameras? If not, do the Met Police carry out radar enforcement? Or is it widely ignored?
Average speed cameras, carefully located so that they cover the whole road regardless where you join and leave. However, someone I know who drives a car similar to mine tells me that driving the Westway with the car’s speed limiter set to 37 will not trigger any enforcement. I also work with someone who claims to do 40 on it every day - he arrives at about 4am, so he’s doing 40 throughout and not encountering the traffic jam at the eastern end - and also never gets ticketed. So I suspect the cameras are still calibrated as they were when the limit was 40. Whether that will eventually change, I don’t know, but I expect it will.

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