20 mph!!!

[Lowlander]

How far do I want to take it? Much further personally, but let's compromise on speed limits.

As to time, how much do you waste on inefficient traffic lights? Some European cities switch them off at night.

Campaign for that and you'll save far more time!

[DaveR]

Entirely unsurprisingly, there is research commissioned by TFL specifically addressing the impact on road safety of 20mph zones. You can find it here:

http://www.tfl.gov.uk/cdn/static/cms/documents/20-mph-zones-and-road-safety-in-london.pdf

I'm sure some of the forum's amateur statisticians will crawl over it and identify where the (professional) statisticians have got it wrong. Nevertheless, worth reporting the conclusions on the effectiveness specifically of London 20mph zones:

The main conclusions are:

? On average, between 1991 and 2006, there has been a 1.7% decline in all casualties

each year on London?s roads.

? Historically, 20 mph zones in London have reduced overall casualties within zones by

42% above this background decline.

? In 20 mph zones there have been reductions for all casualty groups and severities.

? In recent years, the effectiveness of 20 mph zones appears to have decreased, but

those implemented between 2000 and 2006 still reduced casualties by 23%

compared with areas outside 20 mph zones.

? There was no evidence of significant migration of collisions or casualties to areas

adjacent to 20 mph zones.

? For areas with high casualty histories, the benefits of implementing a 20 mph zone

are greater than the costs of implementation. However, in areas with low casualty

histories, building costs are greater than the value of preventing casualties.

[Blah Blah]

It's worth noting the decresed reduction, and that may well be due to the spurt of fitting speeding humps between 1991 and 2000 on roads that genuinely needed them, like outside schools, and dealing with rat runs through residential streets. Then it became fitting speed humps on every residential road used as a through road and so on.

The lack of evidence of migration to surrounding areas/ roads shows how traffic calming in the right places is effective, and kind of proves the lack of need of 20 mph blanket limits. There as yet is no data for the impact of a blanket 20 mph policy as (I've pointed out above) the first borough to introduce that did it in 2013/14 and tfl has published no data for 2014 yet. So I expect the data to not be convincing in boroughs where accident rates were average. I fully expect there to be no significant change or benefit. I would like to see the cost of enforcement too. I'm willing to bet it's prohibitive.

I like Lowlanders point about some cities turning off traffic lights at night. Not sure if that could work in London but see the sense in it.

[DaveR]

"The lack of evidence of migration to surrounding areas/ roads shows how traffic calming in the right places is effective, and kind of proves the lack of need of 20 mph blanket limits. There as yet is no data for the impact of a blanket 20 mph policy as (I've pointed out above) the first borough to introduce that did it in 2013/14 and tfl has published no data for 2014 yet. So I expect the data to not be convincing in boroughs where accident rates were average. I fully expect there to be no significant change or benefit. I would like to see the cost of enforcement too. I'm willing to bet it's prohibitive."

Here is some more research you may find informative:

http://psy2.ucsd.edu/~mckenzie/nickersonConfirmationBias.pdf

"Confirmation bias, as the term is typically used in the psychological literature, connotes

the seeking or interpreting of evidence in ways that are partial to existing beliefs,

expectations, or a hypothesis in hand"

[Seabag]

I agree with speed reduction in principle

But it don't 'arf feel weird

[keekybreeks]

it seems that being made to driver slower is really causing issues with the communities masculinity and your god given right to drive like a real man

good.

[Blah Blah]

Bravo DaveR! Interpretation of data is open to debate. We all know that. And that includes your interpretation as much as anyones. You are speaking to someone with a Phd in psychology here btw ;).

But hard data on number, type and location of accidents can not be interpreted in any other way than it is. Accidents have fallen, but the rate of decrease has fallen too. The reasons will be numerous, but it's also not unreasonable to assume that in the absense of accident blackspots to traffic calm, roads with less risk become traffic calmed. There is no hard data as yet on the impact of making all roads in a London borough 20mph, of which only comparison to previous data of existing 20 mph zones can give any conclusion of impact. I don't see why that's so hard to understand or why you felt the need to post an academic paper on the nature of data and bias.

[spider69]

keekybreeks Wrote:

-------------------------------------------------------

> it seems that being made to driver slower is

> really causing issues with the communities

> masculinity and your god given right to drive like

> a real man

>

> good.

I have seen many women driving like real pr..tts

[Loz]

keekybreeks Wrote:

-------------------------------------------------------

> it seems that being made to driver slower is really causing issues with the communities

> masculinity and your god given right to drive like a real man

What an utterly sexist tosspot of an opinion.

[JohnL]

mako Wrote:

-------------------------------------------------------

> Lowlander Wrote:

> --------------------------------------------------

> -----

> > Sydenham Hill length 3 miles

> >

> > At 30mph - 6 minutes

> > at 20mph 9 minutes

> >

> > Assuming generously that you could drive at

> those

> > speeds the entire length, you'll probably waste

> > more time posting on this thread in frustration

> at

> > the new limits than you'd spend driving at 30

>

> 3 minutes there and back each day and that is a

> couple of whole days every year that you could be

> spending with friends family etc instead extra

> time stuck on a big wide road doing 20. how far do

> you take it lowlander? 10mph limit may mean less

> chance of death. 5mph limit even less chance of

> death. no cars? As mentioned on the other thread

> the last year of full records available for rtas

> (2013) was the lowest recorded number of deaths

> ever. its politically motivated and has nothing to

> do with safety.

Does speed decrease journey times in London though - or

does it just get you to the next bottleneck quicker.

[Lowlander]

JohnL Wrote:

-------------------------------------------------------

> mako Wrote:

> --------------------------------------------------

> -----

> > Lowlander Wrote:

> >

> --------------------------------------------------

>

> > -----

> > > Sydenham Hill length 3 miles

> > >

> > > At 30mph - 6 minutes

> > > at 20mph 9 minutes

> > >

> > > Assuming generously that you could drive at

> > those

> > > speeds the entire length, you'll probably

> waste

> > > more time posting on this thread in

> frustration

> > at

> > > the new limits than you'd spend driving at 30

> >

> > 3 minutes there and back each day and that is a

> > couple of whole days every year that you could

> be

> > spending with friends family etc instead extra

> > time stuck on a big wide road doing 20. how far

> do

> > you take it lowlander? 10mph limit may mean

> less

> > chance of death. 5mph limit even less chance of

> > death. no cars? As mentioned on the other

> thread

> > the last year of full records available for

> rtas

> > (2013) was the lowest recorded number of deaths

> > ever. its politically motivated and has nothing

> to

> > do with safety.

>

> Does speed decrease journey times in London though

> - or

> does it just get you to the next bottleneck

> quicker.

City of London calculate that: Yes. If the average City spot traffic speed of 21.9mph is reduced to 20mph a 1.6-mile journey across the City journey times will increase by 25 seconds.

http://www.cityoflondon.gov.uk/services/transport-and-streets/traffic-management/Pages/20-mph-speed-limit-proposal.aspx

Generally the consensus seems to be 20 seconds per mile

So the question is are people thinking that time savings outweigh the life savings?

[Asset]

[Loz]

Lowlander Wrote:

-------------------------------------------------------

> So the question is are people thinking that time

> savings outweigh the life savings?

Where does that line of thinking stop? Is 15mph even better? 10mph? 5mph? What is an 'acceptable' number of deaths/injuries?

[Otta]

Loz Wrote:

-------------------------------------------------------

> keekybreeks Wrote:

> --------------------------------------------------

> -----

> > it seems that being made to driver slower is

> really causing issues with the communities

> > masculinity and your god given right to drive

> like a real man

>

> What an utterly sexist tosspot of an opinion.

Probably an element of truth to it though.

[Lowlander]

Loz Wrote:

-------------------------------------------------------

> Lowlander Wrote:

> --------------------------------------------------

> -----

> > So the question is are people thinking that

> time

> > savings outweigh the life savings?

>

> Where does that line of thinking stop? Is 15mph

> even better? 10mph? 5mph? What is an 'acceptable'

> number of deaths/injuries?

20mph seems to be the equilibrium in terms of cost/benefit.

Similar on rail and air transport - MH370 disappeared because it's not deemed worth the investment to track planes in real time for a once in a generation incident; and why we haven't got fully automatic signalling across the rail network, because the investment would be billions...to possibly save a few lives.

[Loz]

Otta Wrote:

-------------------------------------------------------

> Loz Wrote:

> --------------------------------------------------

> -----

> > keekybreeks Wrote:

> >

> --------------------------------------------------

>

> > -----

> > > it seems that being made to driver slower is

> > really causing issues with the communities

> > > masculinity and your god given right to drive

> > like a real man

> >

> > What an utterly sexist tosspot of an opinion.

>

> Probably an element of truth to it though.

Most sexist/racist/whatever tosspot opinions usually have an 'element of truth', but it's rarely an acceptable excuse for having them.

[Loz]

Lowlander Wrote:

-------------------------------------------------------

> 20mph seems to be the equilibrium in terms of cost/benefit.

You have a source/reference for that?

[Otta]

Loz Wrote:

-------------------------------------------------------

> Otta Wrote:

> --------------------------------------------------

> -----

> > Loz Wrote:

> >

> --------------------------------------------------

>

> > -----

> > > keekybreeks Wrote:

> > >

> >

> --------------------------------------------------

>

> >

> > > -----

> > > > it seems that being made to driver slower

> is

> > > really causing issues with the communities

> > > > masculinity and your god given right to

> drive

> > > like a real man

> > >

> > > What an utterly sexist tosspot of an opinion.

> >

> > Probably an element of truth to it though.

>

> Most sexist/racist/whatever tosspot opinions

> usually have an 'element of truth', but it's

> rarely an acceptable excuse for having them.

Perhaps not, and I agree that the post was sexist. But take away the gender bit, and I agree that there are quite a number of people out there (male or female) who do seem to think they have some God given right to drive and rule the roads.

[DaveR]

"You are speaking to someone with a Phd in psychology here btw ;)."

But no experience or qualifications in the relevant field, and yet somehow able to confidently predict what the data will show in due course. Impressive.

BTW, I don't have any personal interpretation of the data because, from my own professional life, I understand the difference in relative worth between a lay and professional opinion.

The only real issue here is whether there is credible evidence that the 20mph zones are a reasonable road safety measure. Like anything new, there's no guarantee, and anybody can speculate about reasons why it might not work, but it's glaringly obvious that from a safety perspective it's not unreasonable. From a 'toot toot' Mr Toad perspective, there may be a different view, but I'm not really interested in that.

Edited to answer the question:

"why you felt the need to post an academic paper on the nature of data and bias"

- because I was taking the p!ss

[Loz]

Otta Wrote:

-------------------------------------------------------

> Perhaps not, and I agree that the post was sexist. But take away the gender bit, and I agree that

> there are quite a number of people out there (male or female) who do seem to think they have some God

> given right to drive and rule the roads.

Well, yes, that bit is pretty inarguable.

[Lowlander]

Loz Wrote:

-------------------------------------------------------

> Lowlander Wrote:

> --------------------------------------------------

> -----

> > 20mph seems to be the equilibrium in terms of

> cost/benefit.

>

> You have a source/reference for that?

Yes - it's burgeoning adoption by councils UK wide and public acceptance (~60% in favour). Haven't seen any mainstream arguments for above or below 20mph.

[Loz]

Lowlander Wrote:

-------------------------------------------------------

> Loz Wrote:

> --------------------------------------------------

> -----

> > Lowlander Wrote:

> >

> --------------------------------------------------

>

> > -----

> > > 20mph seems to be the equilibrium in terms of

> > cost/benefit.

> >

> > You have a source/reference for that?

>

> Yes - it's burgeoning adoption by councils UK wide

> and public acceptance (~60% in favour). Haven't

> seen any mainstream arguments for above or below

> 20mph.

Councils are hardly known for using actual evidence. "Something must be done, this is something, let's do it" is more the usual approach. And public acceptance is entirely dependent on what question you ask!

So is there any actual scientific evidence or stats to back the cost/benefit ratio, comparing it to, say 25mph or 15mph?

[mako]

Lowlander, that cost benefit may be a cost benefit to the council, which doesnt make it a cost benefit to everyone else. Does anyone think there will be less 'tosspotts' of any gender as a result of a reduction in speed limit. If not its not really relevant.

[spider69]

Perhaps it might be worth considering that any for or against debate on this subject is a complete waste of time as Southwark will do what ever they want regardless of public opinion.

If you have 7 votes against including the Police and 2 for from the usual pressure groups you should be able to accept that you are being shafted 7 ways to Sunday.

[Blah Blah]

No Dave, I said I have a view of what the data may show but you will see that I make it clear it's a wait and see scenario because we don't know. I swear some people only see what they want to see when reading others posts.

The issue really is about how we change the behaviour of some poor drivers. Sticking 20 mph signs everywhere won't do that, unlike speed humps that (for better or worse) force some kind of alternative action by the driver.