Road Safety News

DfT to commission research into 20mph limits

Thursday 13th March 2014

The DfT is to commission research into the effectiveness of 20mph speed limits in order to “support and inform future policy development on 20mph speed limits and zones”.

In the tender document, the DfT says: “While there is evidence suggesting that 20mph zones are effective in reducing collisions and speeds (as well as leading to other benefits), there is an evidence gap on the effectiveness of 20mph speed limits”.

The new research will set out to “establish the effectiveness of 20mph speed limits, in a range of settings, which is robust enough to attribute any impacts to the scheme”.

In the tender, the DfT says that while monitoring data from 20mph speed limit schemes in Portsmouth and Bristol “indicate potential benefits, the evidence from these studies is inconclusive”.

The project will set out to evaluate the effectiveness of 20mph speed limits in terms of a range of outcomes including speed, collisions, injury severity, mode shift, quality of life, community, economic public health benefits and air quality.

It will also examine drivers’, riders’ and residents’ perceptions of 20mph speed limits and assess the relative cost/benefits to specific vulnerable road user groups including children, cyclists and the elderly.

The study is a three-year project with a final report anticipated in early 2017.

The project is being tendered through the DfT’s ‘transport-related technical and engineering advice and research (T-TEAR) framework’, rather than an open competition. For more information contact Graeme Mateer at the DfT.



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The monitoring of 20mph schemes should have been undertaken by any competent authority in a similar manner to its road safety schemes. The information is there - or should be - so why is the DfT commissioning yet another study. All it needs is for ADEPT to commission a consultant to collect and collate the information from its members and publish a report.
Lance Fogg, Arena Associates Ltd

Agree (1) | Disagree (0)

Eight years ago I was involved in assessing the effect of the introduction of 20mph Zones in Bristol. The results were inconclusive. The casualty and speed reductions that were obtained were not statistically significant. I assumed at that time that the DfT woudl either follow up with further investigations elsewhere or revise their guidelines. They did neither. Instead, the multitude of highway authorities across the country have continued to implement 20mph zones and streets in a rather subjective and random manner, probably with no specific targets in mind other than to placate the local residents and councillors and to appease the political pressure for such measures. Why has it taken so long for the DfT to realise that robustly-based guidelines are long overdue? I suspect mainly because the sound engineering competency of the department has disappeared with continual cut-backs and massive voluntary redundancies. The same lack of leadership and competency also applies to the absence of road safety targets and the very similar manner in which "Shared Space" guidance has been lacking. In the absence of DfT leadership it occurs to me that ADEPT should be taking the lead and promulgating evidence-led guidance in this and other aspects of road safety and traffic engineering. Leadership is long overdue.
Lance Fogg, Arena Associates Ltd

Agree (0) | Disagree (0)

Just a reminder to Terry that low(er) speed limits in residential areas are primarily for the benefit of the residents themselves and non-motorised users of the roads, so promoting 'going slower is better' is rightly in the interests of these people and not the motorised road-user who happens to use the road and who is hardly going to be put out by a lower speed limit.
Hugh Jones, Cheshire

Agree (13) | Disagree (18)

Well it is rather obvious stating 20mph speed zones are effective at reducing speeds, any speed downgrade does that! But is this always a good thing? People and industry want/need to be mobile, not stuck in the past. The 20mph speed limits was abandoned in 1930 as out-dated, even for the primitive old vehicles of the time. Is there any other industry, not just transport, that promotes going slower is better?
Terry Hudson, Kent

Agree (22) | Disagree (14)

Peter Taylor has highlighted the fundamental flaw in 20 limits - getting motorists to observe them. All the potential benefits are academic if driver behvaviour doesn't change. Rather than a three year report, initially comparing before and after speeds in specimen roads/streets would be a good starting point and generally, if there is a significant decrease then okay, they can look deeper into the other possible wider benefits, but if not, the other 'outcomes' mentioned become academic.
Hugh Jones, Cheshire

Agree (21) | Disagree (3)

I welcome this development in the hope that it will properly guide Local Authorities in the matter of 20 mph limits. With a few exceptions the debate has become mired in ideology and anything that reintroduces objectivity has to be a good thing. When a major Local Authority can receive significant opposition to its proposals and react to it as follows: “The overall result of the public consultation appears to be against the proposals but this is an oversimplification of the whole picture.” And then go on to blame the respondents for being the wrong respondents, and for not understanding the issue after they themselves have published reams of biased propaganda in support of it, a few solid facts would not go amiss.
Tim Philpot, Wolverhampton

Agree (29) | Disagree (1)

What do they mean by effectiveness and will there be a need for the research to conclude a positive effect on all the possible outcomes, speed, collisions, injury severity, mode shift, quality of life, community, economic public health benefits and air quality? If it fails in any one will they call them off? I would love to know how they will look at public health benefits when these are already a postcode lottery on A&E facilities and the golden hour.
Peter London

Agree (16) | Disagree (5)

Apart from an oblique reference to assessing "driver's perceptions" there appears to be no assessment of the efficacy (or otherwise) of enformcement in these schemes....?
Peter Taylor

Agree (11) | Disagree (3)

I warmly welcome this investigation, better late than never. But why on earth shouuld it take years to obtain results? Isn't there more than enough data available already? Stats19 and the borders of the existing areas should surely be sufficient at least to see what has happened to accidents and injuries?

It seems to me perfectly sensible to put all new 20mph areas on hold - if as seems to me likely the results are adverse the waste of money will not just be what is spent, but what has to be spent again to remove the signs.

There is absolutely no need for more "trials" - there is already far more data in existence than trials would produce - and no delay would be involved.
Idris Francis Fight Back With Facts Petersfield

Agree (35) | Disagree (13)

How can the DfT justify admitting the evidence for 20mph is weak while, at the same time, encouraging wide-spread 20mph implementation at a cost of £millions?

And why can't the DfT perform the analysis themselves? They have data analysts and almost all the data needed on their systems, they just need the councils to tell them every road that is 20mph, and the date it became 20mph. This should have been done years ago.

But we can solve the entire problem easily. All the DfT has to do is tell the councils they must only install 20mph within scientific trials.
Dave Finney, Slough

Agree (26) | Disagree (11)

If the DfT really believe there is a need for such a report, let's at least hope the consultants will have the expertise to do it properly, otherwise in three years time we'll have yet another inconclusive report, written in non-committal terms.
Hugh Jones, Cheshire

Agree (30) | Disagree (2)

Thanks Eric and Rod.
I think most regular readers know your respective positions on the subject of 20mph limits, so suggest there is no further need for you to elaborate in this thread. I think the vast majority of us will welcome this piece of work by the DfT and will look forward to the final report.
Nick Rawlings, editor, Road Safety News

Agree (34) | Disagree (3)

DfT guidance already requires Traffic Authorities to "consider the introduction of more 20 mph limits and zones, over time, in urban areas and built-up village streets that are primarily residential, to ensure greater safety for pedestrians and cyclists, using the criteria in Section 6." as a "Priority for action".

Already many authorities have implemented pilots and after looking at the wide benefits have implemented on an authority-wide basis.
Rod King, 20's Plenty for Us

Agree (16) | Disagree (26)

The unproven 20mph social experiment is diverting attention, funding and resource from established road safety initiatives, and should be stopped until there is sound evidence to support it.
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (38) | Disagree (23)

If this research is going to take three years to complete then it makes sense to call a halt to the imposition of 20 limits until the results are in. Woe betide the local authority that jumps the gun if the findings prove that 20 limits are more dangerous than 30's and 40's.
Duncan MacKillop, Stratford on Avon

Agree (34) | Disagree (18)

We have long supported DfT conducting ongoing monitoring. At the moment it does not even know the length of 20mph limits or conversions from 30 to 20. And here is the link to watch the video in which Robert Goodwill announced this :-

I suspect it will form the foundation for setting a national default 20mph limit for all residential roads in 2017.
Rod King, 20's Plenty for Us

Agree (11) | Disagree (31)