Road Safety News

Collisions and casualties increase in 20mph zones: IAM

Friday 4th July 2014

The number of serious accidents on 20mph roads increased by 26% last year, according to analysis of Government data by the Institute of Advanced Motorists (IAM). 

The IAM says that the number slight accidents on 20mph roads also increased by 17%.

The figures prompted the IAM chief executive to call for the Government to “take stock on the effectiveness of 20mph signs”.

However, Rod King from 20’s Plenty called the IAM “naïve” for “not taking into account the huge increase in the number and length of 20mph streets and roads”.

The IAM says that in the same period, there was a decrease in the number of serious and slight accidents on 30mph and 40 mph roads. The number of serious accidents fell by 9% on 30mph roads and 7% on 40 mph roads, and slight accidents fell by 5% and 3% respectively.

Serious casualties in 20mph zones also increased by 29% while slight casualties went up by 19%.

Simon Best, IAM chief executive, said: “The Government and councils need to take stock on the effectiveness of 20mph signs. 

“Recent advice, guidance and relaxation of regulations has all been about making it easier for councils to put 20mph limits in place.

“More and more roads are being given a 20mph limit but they do not seem to be delivering fewer casualties. 

“The IAM is concerned that this is because simply putting a sign on a road that still looks like a 30mph zone does not change driver behaviour. 

“More evaluation and research is needed into the real world performance of 20mph limits to ensure limited funds are being well spent.” 

In response, Rod King MBE, founder and campaign director of 20’s Plenty, said: “We are disappointed that a motoring organisation that claims to be a leading road safety charity should be so naïve as to think that an increase in the number of casualties on 20mph roads is indicative of any sort of increase in danger, without taking into account the huge increase in the number and length of 20mph streets and roads.

“In 2012 some gullible organisations made the same claim and it was investigated by the BBC “More or Less” programme which concluded that the large increase in the number of 20mph roads and consequent reduction in 30mph roads would be expected to account for any such change.

“As the DfT holds no record of the changing total length of 20mph and 30mph roads in the UK then no adverse safety trend can be assumed from this increase.

“There is also public health consensus that 20mph is safer than 30mph. Physics proves it. In the distance a 20mph car takes to stop, a 30mph car is still doing 24mph.”


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I don't disagree with cars travelling at slower speeds especially in high residential areas and outside schools etc, however the introduction of 20mph limits in Bristol seem to have gone against all common sense. We now have major, wide open roads with 20mph limits that are virtually impossible to keep to without watching the speedometer constantly.

I would state that this is in itself more likely to increase both car to car accidents and hitting pedestrians.

I have been overtaken and tailgated by irate drivers and cyclists which also seems to be a factor in accident probability.
Les Bristol

Agree (20) | Disagree (1)

If you drive at 20mph rather than 30mph traffic density increases because you can drive closer to the car in front. More traffic in the same amount of space is bound to increase the risk of collision. To reduce collisions between vehicles they need to be kept as far apart as possible not packed into a restricted space. With most vehicle pedestrian collisions being in urban areas where visibility is often hampered by parked cars this too needs to be the focus of attention.
Andrew Pittman, Bristol

Agree (20) | Disagree (7)

The village I live in converted to 20mph just over a year ago and is now policed by a small group of volunteers. I could not support the 20mph in the village when they campaigned as I felt the natural restrictions in the road in the village itself naturally slowed cars and the signs would actually be more of a distraction. Since the signs went up I strictly obey the 20mph and as a direct result have been tailgated (including by a cyclist), and been overtaken in a very unsafe manner on two occasions where they were clearly not doing 20 and also experienced road rage for the first time in over 40 years driving. I honestly believe the chances of an accident in the village have risen since the introduction of the 20 limit. What is more, it is still being reported to the community as being a success.
Sally Westwood, Bradford on Avon

Agree (25) | Disagree (5)

Is the accident rate not increasing in the 20mph zones because most people are now looking at the speedometer more than the road....I know I am. This is not a clever idea.
Greg Fellows

Agree (33) | Disagree (6)

"Our complaint was with the "scaremongering" nature of this followed by the comment "More and more roads are being given a 20mph limit but they do not seem to be delivering fewer casualties.""

Yes Rod, but the thing is, more and more roads are being given a 20mph limit but they do not seem to be delivering fewer casualties. Is anyone thinking about any other solutions? Targeting antisocial/aggressive driving perhaps? But this cannot be defined by a number.

It is simplistic in the extreme to think that the best overall solution to the wide variety of complex and conflicting issues and problems is just a number, and to promote just one solution while being blind to the possibility of other solutions is obsessive and unprofessional, and therefore likely to be ineffective and wasteful, and therefore dangerous.
Dave Taylor, Guildford

Agree (26) | Disagree (6)

That's correct Eric. IAM confirmed that even though they presented all those facts nothing could be concluded from them other than the fact that if you increase the number of 20mph roads then there will be an increases in the total casualties.

Our complaint was with the "scaremongering" nature of this followed by the comment "More and more roads are being given a 20mph limit but they do not seem to be delivering fewer casualties."

Anyone in road safety knows that the the key indicator is the casualties per mile of road and not the overall total. In addition, if the first areas you change from 30 to 20 are those with higher casualty stats anyway then this will skew the results even more.

There is ample evidence within local authorities that pilots and implementations have delivered road safety benefits. Detailed analysis by officers in most of our iconic cities have come to this conclusion.
Rod King, 20's Plenty for Us

Agree (10) | Disagree (27)

More cherry picking, Mr King.
Simon Best's latest press release goes on to say "Our point is that there is no evidence that 20mph limits on their own are reducing casualties and more attention needs to be given to the design of the road and other measures where there is a proven casualty problem. That is completely valid. The 20's plenty’s response is based on a bogus reading of our press release."

I would also add that not only does the original IAM release not "say, or imply, that a 20mph limit increases danger" but nor does it "say, or imply, that a 20mph limit does not increase danger".
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (21) | Disagree (4)

Fair point Andrew.
I think it must be accepted that there will be a lot less than 100% compliance and as physical speed management and enforcement are probably not going to play much of a part, it is down to the goodwill of the motorist to realise the virtue of slower speeds in urban areas. Realistically this is not going to be universal, but from what I have seen in a local signed only 20, there is sufficient reduction in speeds and change for the better in some drivers' behaviour to make it worthwhile.
Hugh Jones, Cheshire

Agree (6) | Disagree (17)

Would someone please tell me how on earth we can expect speed limits which may seem reasonable to residents, but not so to drivers, to be enforced without the assistance of mandatory ISA?
Andrew Fraser, Stirling

Agree (0) | Disagree (10)

I note that Simon Best of IAM now comments:-

"At no point do we say, or imply, that a 20mph limit increases danger."
Rod King, 20's Plenty for Us

Agree (6) | Disagree (18)

The comment that town centres being so congested that 20mph limits were introduced as part of a solution is ludicrous. What point is there for a 20 limit in a town centre where traffic is already crawling along at much less than 20mph? Nothing to do with speed – everything to do with road engineering; restricted turning, pavement build outs; and altered traffic light sequencing.

Parked vehicles forcing traffic to face oncoming traffic in an overtake as a hazard? ; Yes, they are, but Councils nation wide have adopted just such tactics when obstructing one side of a road with a pavement build out extending to the centre with priority to one side of the road –they then call it a “Safety feature”. Speed humps that cause damage to vehicles and discomfort to passengers, increase pollution through braking and accelerating – are likewise “Safety features”.

Such hazards are cursed by almost all and sundry. Only a few ask for them, but in the main, Councils are appeasing those who see road safety as an ever restricting obstacle course designed to cause hardships for essential and emergency services, travellers, and locals alike.
Derek Reynolds, Salop.

Agree (25) | Disagree (6)

Brian. I subscribe wholeheartedly to the enforcement of rules under the Road Traffic Acts including as you say the no parking within 10 metres of a junction. However how can you possibly expect the police to undertake this task when we are reducing the numbers in service.

Further it would annoy a lot of people and some local authorities might have egg on their faces because many years ago they lost the plot and decided to place yellow line around such corners or bends. However they obviously forgot about the no parking distance rule. It would have been easy or easier at that time to cover the 10 metres but they didn't and some stopped far less that that distance. Thus car drivers seeing the end of a double yellow thought that it would be ok to park. Nowadays some local authorities have even made these close to corner areas into parking bays and are making money out of them.
bob craven Lancs

Agree (20) | Disagree (1)

The usual procedure to see if something is giving the results promised by its introduction, is a usual three year before /after statistics. How many 20mph schemes have been introduced with a three year previous known emission data? Which must include vehicle numbers and types. Yet we are constantly told that there is an improvement in air quality with 20mph schemes.
Terry Hudson, Kent

Agree (28) | Disagree (3)

I agree that 20 is plenty. The TfL and IAM if they work together can stop many accidents, if they take into consiseration 2 things from the Highway Code.

1 - Stop parking on the wrong side of the road at anytime as is on the Continent, this will avoid head on collisions with other road users who are using the road correctly.

2 - Enforce Highway Code rules for parking within 10 mtrs of junctions aspecially side roads, as being to close to junctions restricts the view as drivers or pedestrians approach.

These are just 2 things that seem to have been ignored for many years.
Brian Rumbold. London

Agree (13) | Disagree (12)

“There is also public health consensus that 20mph is safer than 30mph. Physics proves it. In the distance a 20mph car takes to stop, a 30mph car is still doing 24mph.”

And this comes from someone accusing the IAM of "naïvety"?

The only thing that seems to be in Rod's equation about what limits should be is the slower something hits you the less it hurts. Not that if the driver is simply paying attention he is unlikely to hit anything whatever the limit is. That pollution and congestion increase with speeds as low as 20. That respect for speed limits is further eroded. That resources are consumed that could have been used for something effective. That productivity (if those limits were obeyed although in general they are ignored) would reduce. That as I have found as a cyclist, I experience more conflict with cars when they travel at the same speed as me rather than passing me.
Dave Taylor, Guildford

Agree (37) | Disagree (11)

Your comment to me should really have been preceded by "In my opinion..." (or suchlike) rather than present it as an absolute fact. As you said yourself, " important it is to base analysis and policies on all the evidence not just what happens to fit a pre-conceived opinion."
Hugh Jones, Cheshire

Agree (14) | Disagree (6)

From 1959 to 1969 GB KSI increased from 85,657 to 96,272 or 12.4% but as vehicle km rose by 67%, KSI per 10bn vehicle km, the real measure of risk, fell by 33% - as has always done. Which confirms how important it is to base analysis and policies on all the evidence not just what happens to fit a pre-conceived opinion.

Hugh - lower speed limits without significantly lower speeds leads to carelessness with or without mobile electronics.

Dave - I would agree in principle were it not for the fact that all the data that is needed already exists. I will make that case within the 150 word limit tomorrow.

2,000 Asthma deaths pa is indeed well over half the road deaths figure - its also well over the entire figure!
Idris Francis Fight Back With Facts Petersfield

Agree (16) | Disagree (7)

I think that what Bobbio refers to is that in places where the amount of traffic has blighted town centres by congestion and emissions then those same highway authorities are putting in 20mph limits in as part of the solution.
Rod King, 20's Plenty for Us

Agree (13) | Disagree (19)

A couple of people have mentioned the wider impact on the local environment that 20 limits make, writing in such a way as to assume the other impacts are positive. Perhaps they are not. I have seen a report that quotes from a letter from the environment minister confirming AQMA (air quality management areas) imposed which coincide exactly with 20mph zones in towns and cities which breach EU rules. Asthma is now killing over 2000 people a year in the UK and rising, which is over half the total killed on our roads each year. 'Safety', what about health? If a side effect of 20 zones is more pollution and more asthma this surely must be taken into account?
Bobbio Chiswell Green

Agree (25) | Disagree (15)

I think you make the mistake of thinking that wide-area 20mph limits are about micro traffic management. Someone sees a sign and responds accordingly. Actually, its about whole communities revaluing their roads as public spaces. Its about developing a social norm that say "20 is plenty and we will only authorise going faster where its safe and the impact on the community is justified". I really don't think you understand the levels of public and community support for lower speeds on residential roads.

I am afraid the "genie is out of the bottle". 20mph limits are widely supported and we are already in transition from the "old thinking" that 30mph was acceptable on residential streets, high streets and where people work, shop and learn.
Rod King, 20's Plenty for Us

Agree (14) | Disagree (29)

As Derek has mentioned, unless we know the details of all the individual accidents that compile these figures, we can't know whether the speed limits prevailing at the time (and compliance with) had anything to do wth the accidents - so what's the point in us, or the IAM guessing and speculating as to their significance or otherwise? I would hope that the individual LAs concerned might have already done such an investigation - it seems to me this is the easiest way to establish the worthiness of the schemes.
Hugh Jones, Cheshire

Agree (13) | Disagree (9)

Hi Pete, you asked “What is DfT getting wrong?” The DfT should be the guardians of our safety when we use the road network. They should at least ensure that local authorities perform competent analysis of interventions and then report the effects (if not perform this task themselves), but they have failed to do this. The absence of good quality evidence has led to many flawed reports, such as the IAM report above, followed by counter-claims by 20sP etc. This is not how any other field of safety engineering operates.

With 20mph (and all major interventions), the DfT should require that local authorities submit proposals for twice the number of 20mph areas than they have finances to implement. The DfT should then select the proposals into pairs that are similar and then randomly select 1 of each pair as “test”, the other as “control”. This is a scientific trial called an RCT (Randomised Controlled Trial).

By randomising the final selection process, all other factors (such as under-reporting in STATS19, RTM (Regression to the mean), other selection effects and all general influences such as changes in traffic volumes, ABS, air-bags, fuel price etc) should be evenly distributed across “test” and “control” groups. This should leave 20mph as the sole reason for any differences. Other measurable outcomes (such as air quality, cycling rates etc) could also be included in the trials.

The beauty of the RCT is that a simple comparison of test and control automatically produces more accurate results than any other method.
Dave Finney, Slough

Agree (18) | Disagree (8)

The whole speed limit debate over 20mph limits being beneficial in residential areas – or ‘zones’ really does show a misunderstanding of what contributes to incidents in the first place. It cannot be taken that all traffic in a 30mph limit area is travelling at 30mph, likewise in 20mph, and so how can such ‘statistics’ mean anything when their origins from ‘tick boxes’ are in doubt?

In many 30 limit areas traffic may be travelling at anything between zero and possibly 40mph (and quite often 20 or less) – all dependant on circumstances. Similarly in 20mph limit areas. The whole issue of introducing such lower speed limits causes concern over what speeds are permitted as a maximum – not as a ‘safe’ speed. Therefore drivers will be looking at their speedometers more often and regardless of how much time that takes – it’s a distraction from the road ahead – and that reduces road safety.

Added to this is the mantra that 20’s plenty, and the public at large will – and especially children being indoctrinated into believing 20 is safe – become more blasé when crossing such zones in which 20 is the limit – that will increase incident rates.

Keep It Simple – safety is an attitude of mind brought about through education, it is not a multi layered speed limit program. I do not condone speeding – exceeding a posted limit, but adjusting speed to meet the requirements as demanded by the situation on the road ahead. It need be nothing more, and the understanding of that is brought about through education – training the mind, not punishing the pocket.
Derek Reynolds, Salop.

Agree (30) | Disagree (5)

It would be helpful if those commenting were to actually look at the press release we did in response to the IAM. This can be seen by clicking the link above or at

You can also listen to the BBC "More or Less" programme commenting on a similar claim made 2 years ago by the Sun at the section on 20mph is 12:20 minutes in.

Quite simply, with the 30mph pool of roads reducing and the 20mph pool increasing from a very small base then an increasing number of casualties in the growing 20mph pool is entirely predictable and provides absolutely no evidence of increased danger.

I was also very surprised that the IAM conflates "zones" and "limits". The DfT report shows no statistics on casualties or length of zones as separate from limits. And whilst with current flexibility on signage and calming the distinction is becoming less relevant, it shows a lack of understanding of the issue from IAM. It also shows that when analysing figures having a body of "expert or advanced drivers" is no substitute for an understanding of basic statistics.

The view of Julian in Cambridge is endorsed by the fact that in some places where 20mph limits are being rolled out then they are being phased in on the basis of current casualty statistics. This means that 30mph roads and areas with higher casualties (such as town centres) will be in the first phases.

I believe that these figures actually reflect the success of communities around the country that are rolling out more and more lower speed limits to make their places better places to be.
Rod King, 20's Plenty for Us

Agree (14) | Disagree (18)

How does Mr Peat know what the driving standard is of another contributor? Is he secretly following us around?
Hugh Jones, Cheshire

Agree (23) | Disagree (3)

The reason why accidents will increase in 20 zones is fully covered on the Drivers' Union web site. The last thing police driving experts want in congested urban areas is drivers not driving to what they are seeing through the windscreen but worrying about a needle and points. Prior to 20s they were already driving below that. What we have now is an increase in average speeds from below 20 to 22, 23 in these areas. When will we learn that there is a massive cost to over-slowing major infrastructure which would save more lives elsewhere or on genuine, as opposed to ideological road safety as behind these 20 zone?
Keith Peat Lincolnshire

Agree (16) | Disagree (23)

A scientific trial would be fairly easy to design, but you couldn't rely on Stats 19 to provide the data. Fresh data would have to be collected using established scientific protocols designed for the purpose. Once you had all the baseline data you could soon work out whether or not 20 zones are 'safer' than 30s.

My worry would be that if such a study were undertaken and came up with the 'wrong' answer would anybody believe the results? We also have to factor in to any scientific study something called the backfire effect which is when the stronger the evidence against a particular point of view, the more entrenched that point of view becomes. I doubt very much that Mr King would accept a study that showed that 20s were not as safe as 30s no matter how robust the protocols and methods used.
Duncan MacKillop, Stratford on Avon

Agree (21) | Disagree (9)

I would like to point out that whatever background Rod King of 20s Plenty is, he isn't an expert driver, he has never dealt with accidents nor prosecuted after them. Much of his campaign is for pure ideological reasons.
Keith Peat Lincolnshire

Agree (23) | Disagree (17)

What surprises me is not the content of the report by the IAM or the replies that this has encouraged but the fact that within this report we have already a reply or response from Rod King. Nobody asked me to add my comments to this matter prior to publication.

Is this not creating a precedence and are we to have Mr King's, or anyone else's attitudes or ideas or replies, however right or wrong or biased, actually added to any matter relating to this or any other road safety issue.

This was obviously done prior to the matter being published that a reply was sought, volunteered or invited from Mr King.
bob craven Lancs

Agree (14) | Disagree (8)

20mph roads will be in high risk urban areas and the number of such roads is rising. So if the number of 20mph roads increased by (say) 30% over the survey period the 29% repored increase in accidents would in fact be a net reduction. Is the alleged 29% increase in accidents based on casualties per mile of road? That surely would be the only fair comparison.
Julian, Cambridge.

Agree (19) | Disagree (1)

You have repeatetly called for scientific trials. It's a fair point, but perhaps you may elaborate by letting us know in broad terms your thoughts on what that might entail. What is DfT getting wrong? In replying I am very interested to learn how real roads and stats19 data can be used to provide a set of controls - real roads are very differemt to a lab. I am making a genuine point here - if we have the brain power on this forum let's get real ideas out there.

Dave: on this occasion would be happy to relax the 150 word limit on your reply if that would help. I think our readers would be interested to hear how you would propose to conduct a scientific trail.
pete, liverpool

Agree (17) | Disagree (0)

The major flaw in IAMs analysis seems to be no account taken of the increase in 20mph mileage, but they also ignore RTM and trend as well. Having said that, the DfT and councils make similar glaring errors in their reports leading to a lack of real evidence and endless futile debate.

The solution is staring us in the face: If all 20mph limits had been implemented within scientific trials, we would now have the highest quality evidence such that the IAM, the DfT, the councils, 20sP, Rod, Eric, all RSPs and the public would all know what effect 20mph has.

But it's not too late, new 20mph schemes can still be implemented within scientific trials. Scientific trials are simple to run, would probably cost less than analysing current schemes and would raise the quality of evidence to the best obtainable. They would certainly be a fundamental shift in road safety but one which I believe both sides could support.
Dave Finney, Slough

Agree (12) | Disagree (12)

The video from the other news item running at the moment: "Students highlight smart phone distraction dangers" could also be used to illustrate the benefits of lower speeds in residential roads.
Hugh Jones, Cheshire

Agree (7) | Disagree (12)

I'm also sure that KSIs increased dramatically from 1959-1969, compared to the 10 years previously.
Steve, Merseyside

Agree (6) | Disagree (0)

I can’t say I’m not disappointed – I can’t say I’m not surprised either. I was hoping that, in the IAM’s defence, there would be some more robust analysis behind this. But there is nothing in the research section of their website to imply that their statement is based on anything substantial and the comments appear only in their newsfeed here: . Their reference point is the DfT’s “casualties involved in reported road accidents (RAS30)” which is where you would start a conversation like this, not end it. They do, in fairness, recognise that further research is needed but it is implicit that 20s are failing without properly supporting that assertion.

There’s nothing inherently wrong with taking the collisions stats by road type and feeling cause for concern, but to question the efficacy of 20mph areas on that basis alone without considering rates of casualty in the context of length of carriageway, miles travelled, collision or casualty type is just inadequate. It has already been assumed here that vulnerable road users are the basis of the increase, but the IAM doesn’t present anything on this in their press notice.

I’m afraid Eric is wrong to suggest that the DfT’s position needs to be revised pending further research. There are sufficient checks and balances in place within Local Highway Authorities to ensure that the ‘relaxation’ is used with due caution. The LHAs are very aware of their powers to restrict their own freedoms to ensure that an apparent laissez faire attitude centrally doesn’t mean a lack of control or good judgement locally. We also need the 20s that are going in now to help provide a decent research base for the DfT.

On a final note, and whilst of course I recognise the principal professional concerns of those who are involved with RSGB and/or who contribute to these discussions, we must start to look at the broader outcomes of highway design – speed management included. To restrict our thoughts only to casualty reduction and ignore the wider public health, transport or environment outcomes attributable our streetscape is imprudent. We may end up making our final, long term decisions about 20mph on the basis of net gains rather than single issues, so we’d do well to start acknowledging those other factors sooner rather than later.
Jeremy, Devon

Agree (44) | Disagree (3)

To paraphrase Rod King, I am disappointed that 20's Plenty should be so naïve as to think that an increase in the number of casualties on 20mph roads cannot be related to encouraging people to feel safer in 20mph limits. This story would be illuminated by an assessment of the typical circumstances in which casualties occur in 20mph - I would expect "stepping into the road without looking" to be high on the list (which would be less common in 30mph).

The DfT has recently commissioned new research into 20mph - they need to reconsider (actually withdraw) their "advice, guidance and relaxation of regulations has all been about making it easier for councils to put 20mph limits in place" until the effects are properly known.
Eric Bridgstock, Independent Road Safety Research, St Albans

Agree (19) | Disagree (32)

Are these statistics a result of the ruthless cull of road safety professionals shortly after the last election? I sincerely hope that they haven't taken a leaf out of Andrew Lang's book: “He uses statistics as a drunken man uses lampposts - for support rather than illumination”.

The reality is that the work done by the professionals was reduced dramatically. I would love to see regional and national statistics of all road user groups in the 3 years before the last election and of course the 3 years after. EE & E has to involve the Education!

Agree (13) | Disagree (8)