Monday, October 12, 2009

20mph limits cut speed, crashes and casualties in Portsmouth

The first city in the UK to introduce 20mph limits on almost all residential streets has seen very encouraging results published in an interim report (Surveyor 1/10/09).

In March 2008, Portsmouth completed a nine-month programme to implement signed-only 20mph speed limits on 410 of its 438km road network.

A report commissioned by the DfT has revealed that on roads where the average speed before the scheme was above 24mph, a reduction of seven mph has been achieved. This change was described in the Atkins report as ‘statistically significant’.

The report also found collisions dropped by 13% and the number of casualties by 15%.

Duncan Price, branch head of road safety at the DfT, said there was ‘general support’ for a ‘substantial expansion of 20mph areas’.

Simon Moon, Portsmouth’s head of transport and street managements, said: “This interim report is limited in what it can say about the 20mph scheme – we’ll have to wait until it has been running for three years before we get the full picture.

“But there are some encouraging signs, especially on roads where speeds were significantly higher than 20mph when we imposed the new limit.”

Darlington Cycling Campaign has been calling for a similar scheme to be introduced in the town at our AGM in February 2007.


David Hembrow said...

20 mph roads are an experiment that is new in Britain. As you report, Portsmouth has 410 km of such roads, and they were quite recently introduced.

Over here in the Netherlands the experiment has been going on for rather longer. There are over 30000 km of 30 km/h roads here. At first they had a significant effect on safety, but the effect has faded over time as drivers have become used to the lower speed limit and break it more often. These roads are over four times less safe now than they were ten years ago.

Lower speed limits are a good thing, but they are not nearly enough on their own to make cyclists safe, nor to make cycling attractive enough to result in significantly more cyclists.

Anonymous said...

We have to be very careful when percentages are used to illustrate improvements, there are very misleading and often used to boost expected, but not actual achieved results.
The 13% reduction in collisions needs to be placed side by side with the number of vehicles using the speed restricted roads. As the scheme has been running since 2006 (I believe), it may well be that there has been a large reduction of vehicles actually using the 20mph roads.
I often see percentage figures such as these bandied about when councils and other local parties are desperate to try and vindicate the often huge amounts of tax payers funding applied and manpower used in devising new traffic schemes to encourage cycling and other forms of sustainable transport.
Darlington’s “Local Motion” which was instigated to promote more sustainable forms of transport by visiting people, schools and printing literature spent (I believe) 790,000 sterling in the year 2007/8, and I bet if you look at figures instead of percentages, has actually achieved very little. What is even more worrying is that it has been running since 2004, what is the total costing to date I wondered rather alarmingly.
I do sincerely hope that I am wrong and good luck with the campaign.
Brian V.

Inconvenient Truth said...

You're both quite right to be sceptical. To what extent can political organisations be trusted to publish "objective" evidence, even when that evidence contradicts their political objectives?

At the root of what we are discussing here lies the question, why are so few people cycling in the UK? The answer is a matrix of reasons - infrastructure, motorist behaviour, culture, fashion, fears of "danger", car industry domination.

The idea that a reduction in the accepted urban speed limit will alone result in better conditions for cycling is, of course, fantasy. But it is one important factor in this complex matrix. Over what, after all, do local authorities have control? Infrastructure and speed limits. A determined assault on the hegemony of the car, by reducing its space, reallocating this for cyclists, and making a start on challenging what is acceptable driving behaviour in an urban context, by reducing speed limits, is at least a start.

I do honestly feel that politicians and "experts" in this country are all at sea at the moment. They refuse to build on the obvious connections between good infrastructure (as David is always so helpfully showing us), motorist behaviour towards cyclists, and the number of cyclists on our streets. So we end up with silly discussions about how motorists drive closer to cyclists using under-specced cycle lanes, than when there are no cycle lanes.

As our film Beauty and the Bike says: Why do British girls stop cycling? It's the infrastructure, stupid.

Anonymous said...

Absolutely spot on!

Brian V.

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