Road Safety News

Birmingham’s agrees 20mph limit for 90% of roads network

Monday 23rd September 2013

Birmingham City Council has confirmed its intention to introduce a 20mph limit across 90% of its road network, according to the 20’s Plenty for Us campaign group.

The council, which has more than one million residents, has reportedly said the default should be 20mph and that this should be introduced through limits rather than zones.

According to 20’s Plenty for Us, the 20mph limit will include all residential roads, those with a designated high street function or ‘secondary shopping frontages’, and roads with school entrances or adjacent to schools.

20’s Plenty says the total capital cost of implementing the 20mph limit is estimated at £7m, but adds that “the value of resulting casualty prevention is reported to be £5m per year, based on a conservative estimate in the reduction of collisions at 78”.

Rod King MBE, founder of 20’s Plenty for Us, said: “With Birmingham city and the City of London becoming the latest traffic authorities committing to wide 20mph limits this creates a pivotal moment in enhancing the liveability, safety and active mobility of our communities.

“This is an opportunity for the DfT to recognise that most of it larger cities are rejecting the idea of the 75 year old 30mph ‘national’ limit for urban roads. It’s time to say that 20’s plenty where people, live, work shop and go to school.

“Local authorities are playing their role in this transformation but it could be implemented far more cost effectively if the DfT were to update its signage regulations so that only the exceptions of 30mph and above needed repeater signs.”

Click here to read the full 20’S Plenty news release.


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I am afraid that you are wrong in most of your comments.

It takes 125% more energy to get from 20mph to 30mph than it does from 0 to 20mph. Hence in any real world situation with braking, congestion points, traffic lights, pedestrian crossings, hazards and obstacles, a 20 mph limit reduces the energy used in acceleration to the speed limit by over half.

And even if you take steady state fuel consumption then across an average of cars there is no more fuel used at 20mph than 30mph. It tends to vary by about +-10% depdendent upon the car used. In any case on a Citroen C4 economy was found to be greater than 90mpg at a steady 20mph.

A recent investigation by Imperial College London for the City of London showed no detrimental effect on emissions. See,d.d2k

You can also download our fact sheet on 20mph and emissions from:-
Rod King, 20's Plenty for Us

Agree (4) | Disagree (2)

On the matter of the proposed introduction of blanket 20mph limits, I would just like to comment that this is not purely a safety matter.

In light of global warming, peak oil and the recent re-classification of diesel emissions as carcinogenic, we must also consider fuel consumption and emissions.

Each time a higher gear is selected, a vehicle burns significantly less fuel (gets better MPG), so counter-intuitively, until speed is up to 40 or 50 mph, increasing speed will reduce fuel consumption for many drivers - by allowing the use of a higher gear.

A pure drop of speed limits to 20mph will therefore tend to increase both fuel consumption and local pollution (though it may still be better than traffic 'calming' measures in this respect).

I don't know by how much this will be when the typical UK usage of cars is considered in terms of the number of miles driven in what would become 20mph zones - it may be small - but this could be estimated, and should be taken into account.
Phil Dixon FAIRSO

Agree (7) | Disagree (1)

Why not a drop to 25mph as a compromise? I think the average driver will be more likely to comply than 30-20mph.
Mark Turner, Tamworth

Agree (8) | Disagree (1)


My comment about variable risk on street did not attempt to address Tim's comment about targeting of spending. This was addressed by my point that it was for elected representatives who were closest to the issues and had responsibility for funding to make the choice. We always point out that the reduction of speeds will be variable depending upon various factors. Some of these are completely independent of any speed limit change.

So it shouldn't come as a surprise that in the course of a 5 year period "several" roads may have had a speed increase. Reasons for this could be the end of previous roadworks, change in parking, revised road layout, etc.

That's why it is officers and members closest to the local situation who are best able to interpret results. They can provide the context and local knowledge which empowers them far more than the use of a telescope from afar.
Rod King, 20's Plenty for Us

Agree (4) | Disagree (5)

Rod, you say: "I accept that besides the core risk of any road there will be additional risks associated with differing conditions. However we also know that the speed reductions vary and are higher on the roads where previous speeds were higher."

Can you enlighten us as to how your thinking here addresses Tim's point about better targeting of spending - you seem to be saying that there may be issues that happen, by chance, to be addressed in a wide area limit.

Also, please don't give the impression that speeds always fall when limits are reduced from 30 to 20; Portsmouth saw speeds increase in several streets after 20 was rolled out.
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (3) | Disagree (4)


I think you are wrong to suggest that I have assumed a uniform casualty risk. I accept that besides the core risk of any road there will be additional risks associated with differing conditions. However we also know that the speed reductions vary and are higher on the roads where previous speeds were higher.

Regarding "after" levels of support and satisfaction I was referencing community before and after surveys. Regarding "doing other things" with the money, then this surely is for the democratically elected representatives to decide. Also bear in mind that much of the funding comes from other than road safety sources due to the wide ranging benefits.
Rod King, 20's Plenty for Us

Agree (3) | Disagree (7)

Rod, your assessement of cost-effectiveness is based on the notion that every metre of road carries the same casualty risk. This is manifestly not so and anyone not fogged by prejudice can see this. But I would not be surprised if most major cities indicate satisfaction with the outcome of their 20 limits. After all, if I had just spent hundreds of thousands of pounds in a fanfare of publicity I would not be expressing doubts about its value after implementation. They would not of course have made any comparison with what else they could have done with the money, just as you won't acknowledge there may be more value in other approaches. People may die as resources are sucked away from higher casualty number and severity locations. What happened to their quality of life?
Tim Philpot, Wolverhampton

Agree (9) | Disagree (3)

I haven't had time to read the entire string here (sorry), but I think that these things often go beyond financial savings or whether more or less people are injured, or what the stats say. I find here in Jersey, lots of people use road safety as an excuse to get speeds down, when what they are really after is an improved quality of life for those that live in the area. I will be interested to see the outcome of this initiative.
Philip Blake, Jersey

Agree (6) | Disagree (1)

I don't need to. We always say that zones are more effective in an isolated way than limits. But them costing 50 times more prohibits their extensive use. It becomes far more cost effective to have a wide-area limit. And so far most of our major cities agree!
Rod King - 20's Plenty for Us, Cheshire

Agree (7) | Disagree (7)

Rod, you still haven't acknowledged that the same report you quote that identifies 72% of people being in favour of 20mph limits also identifies IN THE SAME SENTENCE that 49% are also in favour of traffic calming. Until you do this you have no business suggesting other people are fogged by prejudice or taking facts out of context. The benefits of 20mph limits and zones have been conflated often enough to make anyone uneasy. And when Authorities start putting highly optimistic interpretations on tiny samples of data, it is right to ask why. Birmingham has invested a lot of money in recent years in signs that tell you when you exceed the 30mph limit. Given this acknowledges people's reluctance to slow down, how exactly will reducing the speed limit by a further 10mph help?
Tim Philpot, Wolverhampton

Agree (9) | Disagree (8)

So, Rod, Birmingham Council is quoting results from locations such as Hull who have implemented different schemes, clearly intending to give the impression that 20mph "worked" in Hull and will therefore do the same in Brum. Actually, the last report I saw from Hull was predicting how things would turn out - the fact that there seems to be no later reports suggest all is not well.

But that whole section of the Birmingham briefing is classic cherry picking - only certain types of injuries, or over specific years or even months. No mention of the massive increase in serious injuries in Portsmouth a couple of years on. I analyse these reports and briefings with the clear head of a professional safety engineer, as I am not bound by a political imperative to keep a misguided "20's Plenty" dream (nightmare?) alive. Once again, honesty about the effects on road safety is in short supply.
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (7) | Disagree (9)

Anyone reading the Birmingham report without their eyes fogged by prejudice would observe that the note on reductions of 56% or 90% was from the physically calmed 20mph zones put in by Hull in 2003. It was clearly not attributed to a 20mph Total 20 scheme.

You seem to be constantly distorting the words used by council officers and taking them out of context so that you can portray them as some "big conspiracy".
Rod King, 20's Plenty for Us

Agree (12) | Disagree (5)

Birmingham, evidently assisted by 20 Plenty campaigners, has used a hotchpotch of numbers from various schemes, but with no scientific base. No mention of the most recent figures in Portsmouth, and many numbers with no dates or reference to comparable wider trends and no accounting for regression to the mean. Claims of collision/casualty reduction of 56%, or even 90%, are simple not credible from 20mph limits and do your cause more harm than good.
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (6) | Disagree (8)

I sometimes wonder whether those against 20mph limits actually read our press releases or the links we provide to supporting material.

The report from Birmingham City Council is quite comprehensive and details how it arrived at the £5m figure and 78 reduced casualties. You may not agree with the methodology but the logic is provided. Eric, how come you missed this?

In doing so it does detail the number of collisions in the previous 3 years and quotes this at an average of 2,478 per annum! Duncan, how come you didn't spot that?

In everything we do we always aim to provide references to the appropriate reports or articles.

Rather than shooting from the hip and lambasting Traffic Authority plans, those wishing to comment should perhaps do a little more homework before criticising.
Rod King, 20's Plenty for Us

Agree (16) | Disagree (6)

Rod, speaking as a Birmingham resident, if any consultation has taken place it has not been public in any meaningful sense. And the notion we should be asked our opinions after the decision has been made is clearly nonsense. People may express high public satisfaction with a 1 mph reduction in average speed of traffic achieved at a cost of £7 million but I don't think I will be among them.
Tim Philpot, Wolverhampton

Agree (11) | Disagree (4)

Great! A hard and fast figure rather than a percentage means we can now accurately count the number of casualty collisions both before and after the implementation of the 20 limits. Strange then that the press release doesn't give the current number of injury collisions during the previous 12 months so that the comparison can easily be made.

Mind you, all that money for a predicted .000078% improvement looks like money well spent and if it were my 7 million quid I would want to see something a bit better than that.
Duncan MacKillop, Stratford on Avon

Agree (7) | Disagree (5)

I will check how Birmingham derived their 78 collisions and also their £5m a year. I sense a large helping of wishful thinking - that was certainly what I found in Liverpool and Lancashire.
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (6) | Disagree (12)

Rod and Eric

Apologies from the editorial team - the figure should have read 78 and not 78%. A mistake at our end - by me in fact! Now corrected.
Nick Rawlings, editor, Road Safety News

Agree (3) | Disagree (0)


If you did read our Press Release you will see that we reported that the Birmingham report said 78 per year. Their figures not ours. This has therefore been incorrectly quoted by RSGB as 78%.

I think that the councillors in Birmingham have been asking their residents. And if you read the report (mentioned in our press release) you will see that they intend to continue to do so. Everywhere 20mph limits have been implemented resident satisfaction is high and gets even higher after implementation.
Rod King, 20's Plenty for Us

Agree (10) | Disagree (6)

No wonder the funding of public services is in crisis. According to this news item, 20’s Plenty says the total capital cost of implementing the 20mph limit is estimated at £7m, but adds that “the value of resulting casualty prevention is reported to be £5m per year, based on a conservative estimate in the reduction of collisions at 78%”.

This calculation must be challenged as it implies equating costs and values, which is invalid. This is the road to bankruptcy. It is also suggesting significant casualty reductions for which there is no supporting evidence that would stand up to independent scrutiny. An evidence led, well informed public debate on 20mph and road safety is long overdue.
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (10) | Disagree (12)

What a pity no-one appears to have thought to ask the people of Birmingham before committing to this course of action.
Tim Philpot, Wolverhampton

Agree (14) | Disagree (6)

Evidence of the effects of 20mph on road safety is not very good, let alone the effects on air quality etc. If councils continue to spend £millions of tax-payers money on unproven interventions, the public would have a right to be extremely angry if 20mph turned out to be a waste of money or worse, caused serious injuries to increase.

20mph needs to be introduced in scientific trials known as Randomised Controlled Trials. They are simple to run and the effects of 20mph would be clear for all to see. Not just the effects on road safety, air quality changes could also be assessed scientifically with the trial.

If 20mph areas had been installed within scientific trials from the start, there would be no need for the continued confusion and debate over what effect 20mph actually has, we would known for certain.
Dave Finney, Slough

Agree (8) | Disagree (14)