Road Safety News

Road Safety News to review evidence on 20mph limits

Thursday 19th September 2013

Nick Rawlings, editor of Road Safety News, is to conduct a high level review of the evidence with regard to the effect of 20mph limits/zones on casualty figures.

The announcement follows numerous discussion threads on the subject punctuated by claims and counter claims by supporters and opponents of 20mph limits/zones.

Nick Rawlings said: “I decided to conduct the review following a reader comment by Neil Hopkins, Sussex Safer Road Partnership.

“Neil suggested that it would be helpful to see what the evidence tells us, rather than relying on the opinions of individuals and organisations with a publically-stated position the subject.

“There are several research studies and papers in the Road Safety Knowledge Centre that will be included in the review, but we are also keen to hear of other studies that people think should be included.

“We will only include UK-based studies by academic institutions and bona fide research companies, not those carried out by individuals, lobby or campaign groups, or other organisations with a vested interest in, or stated position on, the subject.”

Anyone interested in putting forward a paper should email details to Nick Rawlings as soon as possible. A summary of the outcomes from the review will be published on this newsfeed in early-mid October.


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Is no one actually going to stand and argue for retaining 30mph? Having listened to this debate for years, forgive me for sensing that countless people are being very one-eyed about this......
Lee Williams, Birmingham

Agree (3) | Disagree (0)

I agree with Nadeem. We have never seen 20mph limits as a "magic bullet". Authorities implementing wide-area 20mph schemes tend to do it alongside other interventions which may well include engineering, engagement, travel to work plans.

And we have long argued that the cost of 20mph schemes should not come solely from the "road safety budget" but that source of funds should be aligned with the wide benefits of such schemes. See and

What many local authorities are doing is seeing Total 20 ticking a large number of boxes across many areas of responsibility, including health, equality, accessibility, emissions as well as road safety. In those circumstances it is seems perfectly reasonable to favour that which gives the best and widest benefit to society.
Rod King, 20's Plenty for Us

Agree (9) | Disagree (6)

I think there needs to be a clear distinction between 20mph and casualty reduction. Casualty reduction has a specific objective, whereas the argument presented by Rod et al has many dimensions and has tended to cloud the waters of logical debate. I think organisations that support 20mph zones should use their success to lobby the real resource opportunities in line with their arguments on health & wellbeing and liveability, so that what little casualty reduction funding remains can focus on addressing actual collision hotspot sites where people have already been killed or seriously injured, rather than being preventative measures at other sites. 20mph isn’t the magic bullet to solve all casualty reduction or road safety related issues as some people will have us believe, but unfortunately it seems that in some situations current lobby activity seems to have overridden sensible debate. 20mph firmly remains within the casualty reduction toolkit alongside many other measures.
Nadeem Mohammed, Greater Manchester

Agree (16) | Disagree (1)


I think that such a review will have too narrow a focus. It is suggested that it is restricted to casualties and:-

“We will only include UK-based studies by academic institutions and bona fide research companies, not those carried out by individuals, lobby or campaign groups, or other organisations with a vested interest in, or stated position on, the subject.”

Then this will exclude all of the following:-
• Reports from other countries where 30km/h limits have been used for some time
• Reports from traffic authorities who have implemented 20mph limits and zones both authority-wide and as pilots.


• Any analysis of emissions which are known to have an effect on public health
• Any analysis of modal shift to walking or cycling which is known to have an effect on public health.
• Any analysis of noise levels which are known to have an effect on public health.

The fact is that many local authorities and organisations do have a “stated position on the subject” because they have looked at the wider evidence. To preclude their experience from being included in this review because of that would not reflect the wider responsibility of those charged with setting speed limits.

The two issues seem to be:-

• Should it include reports from local authorities in UK and abroad to gain a wider understanding of casualties.
• Should it include reports which look at emissions and other public health factors.
Rod King, 20's Plenty for Us

Agree (15) | Disagree (4)

Here in Northern Ireland having had a bit of a "discussion" with a 20mph campaigner, a private members bill introduced into the Northern Ireland Assembly (this may fail as the MLA has resigned) for 20mph speed limits in all urban areas - with exceptions - and our Road Services as part of the Government's Road Safety Strategy to 2020 trialling 20mph zones in some locations, this planned review is most welcomed.
Trevor Baird Northern Ireland

Agree (8) | Disagree (1)

I suspect in common with most readers, I have been both amused and bemused at the spats between Rod and Eric.

I suspect that there is very little if any scientific evidence available to prove or challenge the assertion that a 20 mph speed limit is safer than 30 mph. Because of Rod’s brilliant political campaign I, like Dave Finney, think that there is little appetite among politicians or road safety professional bodies to prove or disprove the KSI benefits of 20 mph zones.

Much is said about the social and environmental benefits of 20mph zones, especially for pedestrians and cyclists. I hope in years to come we do not find out that by slowing vehicles down we have actually exposed the pedestrian population to more carbon monoxide, nitrogen and evaporative emissions.

I draw readers attention to a MIT study published last year in an issue of Environmental Science and Technology where they claim that every year, 13,000 people in the UK die a premature death due to emissions from cars, trucks, planes and power plants.

I look forward to reading Nick Rawlings review but I doubt whether it will be conclusive.
Charles Dunn

Agree (16) | Disagree (5)

"Casualty figures alone are not a good way of measuring road safety". I'm afraid this is one of the tenets of 20's Plenty, who talk about "benefits beyond road safety" (I note another comment about air quality). The problem is that detrimental effects on KSI then seem to get ignored or denied.

Separately, there seems to be assumption in Nick's terms of reference that "academic institutions" and "bona fide research companies" are free of vested interests - that is not necessarily the case.

Finally, of the reports that I have reviewed, none has been able to separate out the effects of speed limit reduction from engineering changes. I look forward to the conclusions of a balanced review!
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (15) | Disagree (7)

Casualty figures alone are not a good way of measuring road safety, which has to be looked at in a holistic way. If lower traffic speeds allow more cycling, walking and access to the roads for vulnerable groups such as unaccompanied children, this has to be measured as well. It's time to rethink the dogmatic belief that zero KSI = a safe road.
John Morrison Sevenoaks

Agree (11) | Disagree (9)

Great idea, but you can't review 'evidence' without first working out what actually constitutes evidence in the first place. So, I'll ask, what does constitute evidence? I'll be intrigued to hear the answer.
Duncan MacKillop, Stratford on Avon

Agree (13) | Disagree (0)

Good to hear - thanks Nick. I, and no doubt many others, will await the outcome eagerly.
Will you also be looking at air quality? I only ask as I have heard mention of the fact that the newest diesel bus/truck engines are more inefficient at 20mph than 30mph, with the same going for cars of all ages where 20mph is far lower down the torque curve (thus less bang for buck so to speak). Equally with other issues, I haven't seen conclusive proof one way or the other.
Neil Hopkins, Sussex Safer Roads

Agree (13) | Disagree (2)

This is a great idea Nick although we might need far better evidence than actually exists. The Head of Road Safety Statistics Department for Transport said "there is no specific national information on where all 20mph zones and limits are located. Therefore evaluating the changing relationship between accident rates, travel behaviour, wider health impacts and 20mph zones is challenging.”

But the real issue is the lack of scientific trials and the reluctance to even consider them. If scientific trials found 20mph reduced serious casualties this would silence 20mph critics, but what are the political implications if 20mph increased serious casualties?

Running scientific trials (for any intervention) would be a fundamental change in road safety. The actual effects of interventions would be seen for the first time and I'm not sure the road safety authorities are ready for the implications that could follow.
Dave Finney, Slough

Agree (13) | Disagree (6)