Road Safety News

Lib Dems back 20mph limits

Thursday 16th August 2012

In the latest twist in the debate about the merits of 20pmh zones/limits, the Liberal Democrats have put forward plans to cut speed limits from 30mph to 20mph in residential areas, according to the Telegraph.

The Lib Dems say the proposal, which will be voted on at their party conference in September, is designed to cut the number of road deaths and encourage more parents to allow their children to walk to school.

But the AA warned that while it was not opposed to 20mph limits where appropriate, a blanket introduction would be “totally impractical”.

The motion to be discussed at the Lib Dem conference reads: “Among EU member states, the UK has one of the poorest levels of children walking or cycling to school.

“Many parents cite danger from fast-moving traffic as a reason for not allowing their children to travel to school on foot or by bike.

“Lowering the normal residential speed limit from 30mph to 20mph would make roads safer; in particular a study by the Transport Research Laboratory has found 20mph limits decrease child pedestrian deaths by 70%.

“It has been shown that half of people hit by a car at 30mph will die and only 10% of people hit by a car at 20mph.”

Recent figures released by the DfT show that while deaths and injuries in 20mph zones rose last year from 1,827 in 2010 to 2,262 in 2011, they fell by 1% in 30mph areas. However, the number of 20mph zones across the country will have increased considerably during 2011.

A spokesman for the AA said: “Converting all roads to 20mph would be totally impractical and would impact on driving times and add to costs and delays.

“It’s great in pedestrianised areas, but just slapping up 20mph signs would not make things safer.”

The Association of British Drivers (ABD) took a similarly sceptical stance, saying they “deplore” the idea, citing a lack of evidence. Brian Gregory, ABD chairman, said: "As with most pet road safety ideas proposed by amateur enthusiasts - speed humps, speed cameras etc - there is little attempt to collect scientifically sound evidence of the benefit of such ideas. No proper controlled, "double-blind" trials are undertaken.

“The enthusiasts rely on the strength of their rhetoric and the use of selective data to make their case. Don't be fooled by these methods but look at the facts. And remember that all road safety schemes should be cost justified because if there are better things to spend the money on, then that is where the limited funds should be spent.”

Click here to read the full Telegraph report.


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I disagree with Idris. The whole claim is the more 20 zones the safer it will be. So surely it's perverse to now claim that accident rates have gone up because of too
much or too long or more 20 zones? That supports the expert opinion that 20 zones will increase accidents, and so the more we have the more there will be? Reduce them and the accidents will go down again is the obvious solution.

We predicted that 20 zones would increase accidents and average speeds in congested areas and they have done exactly that. Where's the dispute?
Keith Essex

Agree (1) | Disagree (5)

The TRL & DfT have used percentages because child accidents, & that includes slight, are in reality so low in BUA. Asked by me how many actual accidents, and they both confessed very few. TRL told me 1.45 per zone per year average. However this includes bad problem areas where the issues should be addressed but this does not mitigate throwing blankets over whole areas where no accidents are happening.

In any case I predicted in early 2011 that 20 zones are counter productive and will cause accidents. Latest figures are proving me correct.

To say that this is down to the increase in area of 20 zones, is actually supporting that. In effect the more 20 zones the more accidents? Surely that is in line with my prediction. So reduce 20 zones and they will reduce too then?

I detail at why 20 zones are counter productive.
Keith Essex

Agree (1) | Disagree (4)

My apologies for any confusion caused by my (admittedly slightly flippant) 3-word post last week. It was an instinctive reaction to the news that the Lib Dems were about to pitch into the 20mph debate on what appeared to be a confused premise (and on this point, Idris, I do agree with you). This was enough to rattle even my legendary composure, in a week where I had already made two lengthy posts urging a rational approach to the matter. Why did people like it? You would have to ask them. Maybe they understood and agreed with my reasoning. Or maybe they were just glad it was 147 words shorter than usual...
Tim Philpot (with one "T"), Wolverhampton

Agree (4) | Disagree (1)

We shall soon have gridlock and nothing moving in the UK. Will the last driver please switch off all the traffic lights!!! Couldn't agree more with Nigel.
REMEMAN, Derbyshire

Agree (4) | Disagree (4)

..and if they want to spend mony on road safety, get pro-active traffic units back on the roads.
Nigel Albright

Agree (9) | Disagree (0)

It is not clear what part of this page - the article or the comments - that caused Tim Philpott to run out of words. Nor therefore what the 4 people who liked it actually liked.

One important point that again seems to have been missed is the difference between 20mph zones, with traffic calming and/or enforcement, and 20mph areas with neither. As I understand it the evidence of zone benefit is far more impressive than area benefit, but the danger seems to me perhaps that the LDs, not appreciating the difference - though the DfT certainly does - seem to be calling for 20mph areas ie signs only, in the mistaken belief that they will achieved the benefits provided by zones.

Would such a mistake be surprsing? Given that the LDs did in Portsmouth, not in the least!
Idris Francis

Agree (3) | Disagree (6)

Get caught up in statistics, if you want to. But the base line is that even if this were a good idea there is enough frustration and sometimes aggravation from drivers behind if you stick to 30s in a 30zone. Not only frustration but the result of this is often impatient behaviour such as overtaking which, not uncommonly is done dangerously. Imagine what it would be like if it all came down to 20s. Improving road safety? No, quite the opposite would be the effect in my view. It's just another case of politians who don't know what they are on about putting in place ideas which look politically good but, which are fundamentially flawed and all primarily to try to gain favour of the public. If they are really serious about road safety then all they have to do in promote the enforcement of key elements which already exist in the Highway Code. It's all there, if only they understood it.
Nigel Albright

Agree (7) | Disagree (3)

I am not absolutely sure which reports are being referred to - I just took the % child casualty reductions and searched for relevant reports that contained these findings - these three seemed the closest fit and I think are the most liely ones but I haven't worked through them all myself.
Honor Byford, North Yorkshire

Agree (1) | Disagree (0)

Thanks Honor, though TRL215 is surely not the report the LibDems refer to?

TRL215 states "Child pedestrian ... accidents fell by 70"% (p4) but this does not take account of site-selection effects and reduced traffic flow of "4 to 73"% (p29), possibly partially due to the new by-pass.

Have the Lib Dems confused child accidents with child fatalities? And perhaps they have not understood that the accident reductions were not due to the 20mph schemes?

One puzzle that the report raises is Fig.13 (p30). That graph shows "Accident change (%)" going down to -150%. How is that possible?

Also, their nominal trend line in Fig.13 would probably fit the data better if it were simply a horizontal line at around -60%. The reductions would therefore occur no matter what the speed change was, even if speeds went up!

TRL215 does not demonstrate any safety improvement attributable to 20mph.
Dave Finney - Slough

Agree (3) | Disagree (5)

I think the references you require are as follows:
1. Webster, DC and Mackie, AM, Review of traffic calming schemes in 20 mph zones, TRL215, 1996

2. Brightwell, S. Hull Reaps Road Safety Rewards From Slowing the City's Traffic, Local Transport Today: 10-1. 2003

3. Chris Grundy et al Effect of 20 mph traffic speed zones on road injuries in London, 1986-2006: controlled interrupted time series analysis BMJ 2009;339:b4469
Honor Byford, North Yorkshire

Agree (1) | Disagree (0)

Can anyone tell me which TRL report makes the claim "20mph limits decrease child pedestrian deaths by 70%"?

I'm surprised there are sufficient numbers of child pedestrian deaths in 20mph areas to conduct a statistically significant analysis.

And where can I find this report? I've tried the TRL site but haven't found it.
Dave Finney - Slough

Agree (4) | Disagree (5)

Words fail me.
Tim Philpot, Wolverhampton

Agree (7) | Disagree (1)

I have just put a much longer comment on the Telegraph report than I would be allowed here, so will not repeat it here. I will however include just this one point:

20's Plenty are of course right that because casualties have not been adjusted for traffic volume x distance, there is no evidence that the real risk has increased. But by the same token, neither is there any evidence that it has fallen.

Incidentally, the DfT have confirmed that they do not have that volume x distance data - it's not that they ignored it, its very much a case of reporters misrepresenting the data because they do not understand it.
Idris Francis

Agree (10) | Disagree (8)