Road Safety News

20mph limits have lowest level of compliance

Friday 1st July 2016

84% of car drivers and 83% of LGV drivers exceeded a 20mph speed limit during 2015, according to new figures from the DfT.

Published yesterday (30 June), ‘Free Flow Vehicle Speed Statistics’ reveals that 20mph roads had the lowest level of speed limit compliance in 2015. 16% of car drivers broke a 20mph limit by more than 10mph, while 31% exceeded the limit by between 5-10mph.

30mph limits were the second most flaunted, with 52% of car drivers exceeding the limit during 2015.

This DfT Statistical Release presents estimates of traffic speeds in free flowing conditions on roads in Great Britain. The DfT says the statistics ‘provide insight into the speeds at which drivers choose to travel and their compliance with speed limits’.

The estimates are based on speed data collected from a sample of the DfT’s automatic traffic counters (ATCs), excluding locations where external factors might restrict driver behaviour (junctions, hills, sharp bends and speed enforcement cameras etc).

Despite the figures for 20 and 30mph limits, the bulletin says that since 2011 the percentage of vehicles exceeding the speed limit has generally declined. It also shows that average free flow speeds for all vehicle types across each road type have remained ‘broadly stable’.

On motorways, 46% of both cars and light commercial vehicles (LCVs) exceeded the speed limit (70 mph), a ‘small and steady’ decrease from 2011, when the figure was at 49% for both vehicle types.

Of all road types, national speed limit single carriageways had the highest level of speed limit compliance, with 92% of cars not exceeding the 60mph limit.

44% of heavy goods vehicles (HGVs) exceeded the speed limit on 30 mph roads, while on motorways 99% of HGVs complied with the 60mph limit.

The bulletin also gives details of collisions where ‘exceeding the speed limit’ was reported as a contributory factor.

In 2014, for all accidents, 2.5% of vehicles had exceeding the speed limit as a contributory factor allocated, while for fatal collisions this rose to 9.7%. 

The report also reveals that there were 743,000 fixed penalty notices (FPNs) issued for speed limit offences in England and Wales in 2014, a year-on-year increase of 4%.

FPNs for speed limit offences accounted for 73% of all motoring FPNs in 2014, with the majority (90%) detected by speed cameras.

In 2015, more than 1.2m drivers attended a speed awareness course in the UK. The bulletin says attendance has increased year on year since 2011 ‘due to more police forces joining the scheme, and not solely due to more offences being committed’.



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The calculation for how many lives are saved should be carried out in "Life hours". If the mean lifespan is 75 years then that needs to be converted into hours which accounting of 18.75 leap years calculates to 657,450 hours for a full life (obviously this reduces as time passes, but you get the picture).

The next thing we need to know is the length of the stretch to which the reduction will apply; the mean speed before the imposition of the reduction and the number of driver that are using the stretch of road that is to have a lower speed limit imposed. Say for example 10,000 drivers a day (416.667/hour) travel at a mean speed of 36MPH and for ease of calculations the length of the stretch of road to which the speed limit applies is 1mile. We can now calculate that each driver takes 0.027 hours to travel along this stretch of road.

Now if the same number of people use the road after the speed limit is imposed and as a result of the new limit the mean speed drops 10MPH then we can calculate that it how takes each driver 0.038 hours to travel along the same stretch.

What we have to do now is find out how long it takes for the number of drivers that use the road in an hour (in our example this is 416.667 which gives us 11.57 hours at 36 and 16.026hours at 26. By deducting one from the other we can now calculate that drivers lose 4.45 life hours for every single hour that the lower speed limit is imposed.

According to national statistics the number of lives saved as a result of the imposition of lower speed limits is 0 so that makes our life hours saving by preventing death calculation a simple one.

So that is 4.45 life hours lost; 0 life hours gained. Clearly demonstrating that the imposition of the lower speed limit is having a significant adverse effect on human life.
Libertarian Voive

Agree (0) | Disagree (0)

30 mph limits are generally reasonable, and a responsible motorist will drive more slowly if the situation warrants it.

On the other hand, I find myself increasingly disgusted at the proliferation of 20mph zones. In particular, I know of several in Sheffield where:

- the road is wide and uncrowded
- pedestrians cross carelessly at an angle with their backs to the oncoming traffic and their attention on their smart phones

As a result, we crawl at a snails pace in order to protect the feckless.

In general, 20mph seems to be a sign that all of the responsibility for road safety is being given to motorists, and none to pedestrians. No wonder nobody respects it.
Andy, Sheffield

Agree (5) | Disagree (2)

It's because they're pointless. They're introduced in areas where there have been no road accidents attributable to speed (or certainly not to people driving at 30). I drive through several 20 zones at 30 every day. I was taught to drive a car at 30. 20mph limits are regressive and backward.

Agree (5) | Disagree (2)

"Of all road types, national speed limit single carriageways had the highest level of speed limit compliance, with 92% of cars not exceeding the 60mph limit."

So, on most roads in the country, with a wide range of potential conditions, drivers appear to pick an appropriate speed that is less likely to be above the posted limit. 92% is well above the 85th percentile rule that is/was generally considered a good indicator of a reasonable speed limit.

"In 2014, for all accidents, 2.5% of vehicles had exceeding the speed limit as a contributory factor allocated,"

Well, that kicks the usual interpretation of the "speed kills" lie firmly out of the field.


"There is too much of this atttitude which seems to prevail amongst motorists of only obeying rules when it suits them, as if they know better, which sadly they don't."
On the contrary, driving is a process of constant assesment, which means that a competent driver will pick their own suitable "speed limit" for the mooment.
"Too many don't even go to the trouble of finding about what the rules are they're supposed to be obeying in the first place!"
Given how complex some aspects of traffic law can be, it is not unknown for professionals such as lawyers and that dying breed the traffic cop to not know what a specific rule may be without reference to a book or colleague.
Steve, Watford

Agree (6) | Disagree (1)

I would say we do need regulations. Having said that, year on year reductions in limits to chase lower casualty figures have failed spectacularly. From 2011 only natural variation in casualty figures on the roads and yet proliferation of 30mph changing to 20mph limits, national limits going down to 50 or 40mph. The consequence of such is people start to ignore rules which do not seem logical or actually safe as at slower speeds there is a false perception of safety and therefore attention to the task in hand slips. I can give far, far too many examples of 20mph limits on inappropriate roads. I can also point to many national speed limit roads where I wouldn't dream of going faster than 30-40mph.

I think the point I am trying to make is over zealous speed enforcement and lowering of limits time and time again is not and will not work without a police state like enforcement which I hope you would agree is neither appropriate or desirable. If it is road safety that these schemes are aimed at improving then why after years of them not working do we not look for a fresh approach and new ideas?
Steve Armstrong, Halifax UK.

Agree (10) | Disagree (3)

The evidence is there if you look for it Charles - out on the roads!
Hugh Jones, Cheshire

Agree (3) | Disagree (2)

Hugh, there is no evidence for your assertion that "traffic and motorists need regulating", quite the contrary I think - it is the last thing they need if we are to enjoy safe, equitable and uncongested roads.

Sure some restrictions, such as weight limits for weak bridges and height limits for low bridges may be desirable, but most of the other regulations are part of the cause of our road problems rather than part of the solution to them.

AFAICT, one of the biggest (perhaps *the* biggest) causes of deaths, injuries, damage and congestion is the priority system we operate - giving de-facto priority to traffic on "major" roads over side roads and pedestrians, regardless of who got there first. The response to the problems caused by this poor idea was not to scrap the idea, but was to install traffic lights, roundabouts, pedestrian crossings, etc. to try to ameliorate the problems it caused. And it is at these very "solutions" that most crashes occur. Why? Because they rely for their success on the laws of human nature being suspended - never a good idea.

In places, such as Seven Dials, where some of the "solutions" have been removed, the roads function in a safe, fair and sociable way as they should do, and congestion is reduced for free - win-win.
Charles, England

Agree (4) | Disagree (2)

Fairly obviously Charles, I was referring to conventional roundabouts i.e. 'regulated' where the driver is directed to go clockwise. Similar to speed limits, where the upper limit is 'regulated' as are weight restrictions, one-way streets, parking restrictions etc. etc. they're all there for a reason - traffic and motorists need regulating.
Hugh Jones, Cheshire

Agree (3) | Disagree (1)

Hugh, have you ever seen the "roundabout" at Seven Dials in Covent Garden? You go whichever way you choose. Unlike the pedestrians and cyclists, most drivers do choose to go clockwise, from habit I suppose, but every now and again a car or van does go the other way - and it works exquisitely!
Charles, England

Agree (1) | Disagree (2)

Try driving on the wrong side of the road or anti-clockwise around a roundabout Charles, and see how far you get 'unfettered by regulations'!
Hugh Jones, Cheshire

Agree (3) | Disagree (1)

Rod, do you think that Monderman's schemes would have failed without the speed limit signs? Monderman reluctantly tolerated those signs because they were required by Dutch law, even though they were redundant. They were political not functional.
Charles, England

Agree (1) | Disagree (1)

I find it not uncommon for those opposing 20mph limits to quote Hans Monderman and the reduction of signs, etc. But they do so in ignorance of the fact that a necessary foundation for him making any such reduction in street signage and "rights" was a 30km/h speed limit for the areas concerned.

Note that the DfT is doing what we have been campaigning for. That is for Atkins to consolidate all the evidence that exists from separate traffic authority implementations in a consistent analysis that covers the wide range of benefits that come from slower speeds.
Rod King, Cheshire, 20's Plenty for Us

Agree (5) | Disagree (4)

Hugh, you seem to be saying that you think it is reasonable that the safety of our population should rely on all motorists always and unfailingly complying with all traffic legislation. Do you really believe that? Our understanding of human nature should tell us that it is unreasonable to expect 0% human error in any aspect of human endeavour. For this reason alone, it is clear to me that a system which relies on 0% human error, 24 hours a day, 365 days a year for its efficacy is a seriously flawed system. The evidence that supports my belief is published each year in the RRCGB report.

Hans Monderman proved decades ago that normal natural (unfettered by regulation) human interaction and caution delivers a safer and more pleasant environment for motorists, pedestrians and cyclists than we can possibly achieve by the use of conventional traffic regulations and controls.
Charles, England

Agree (3) | Disagree (4)

One more comment if I'm permitted - the fact that 20 limits on residential roads (or 30s for that matter) are not complied with as much as would be desirable, should be seen as a poor reflection on the motoring public and not as a failing or 'the fault' of the authorities and organisations that promote them. There is too much of this atttitude which seems to prevail amongst motorists of only obeying rules when it suits them, as if they know better, which sadly they don't. Too many don't even go to the trouble of finding about what the rules are they're supposed to be obeying in the first place!
Hugh Jones, Cheshire

Agree (5) | Disagree (8)

Rod, if there is any convincing evidence that unenforced 20mph limits make any significant difference to traffic speeds, why do you think that the government concluded in early 2014 that "the evidence from these studies is inconclusive", and even committed money to fund further research? (as reported here:
Charles, England

Agree (8) | Disagree (2)

Just imagine the outcry and the attention from the media these revelations of non-compliance with rules and regulations would generate if it did not apply to motorists, but others with responsibilities for public safety i.e. aircraft pilots, ships' captains, train drivers, electricians, gas fitters, medical staff, workers in the nuclear industry, construction workers etc.
Hugh Jones, Cheshire

Agree (7) | Disagree (3)

Charles and R

May I suggest you actually read the report I provided the URL for. You are in fact both wrong. 20mph limits can be put on roads where the average speed is greater than 24mph. In fact in the very first wide-area 20mph implementation in Portsmouth the report by Atkins concluded (and I quote ): "For example for the group of sites monitored with average speeds of 24 mph or more before the scheme was introduced, the average speed reduction was 6.3 mph."

Where before and after speeds are measured then the reduction in ave speed is greater on roads which have a higher average speed. Of course on roads where the ave speed is less than 20mph then one would not expect so much of a reduction. It is this spread of reductions from 6.3mph on faster roads to 0mph on slow roads which creates an average of about 1.5mph.

When this reduction is considered across all roads in a network then it provides far greater effectiveness in terms of speed reduction per mile per cost of implementation.
Rod King

Agree (6) | Disagree (8)

Rod, no, the 6mph speed difference wasn't a result of changing the speed limits from 30 to 20, quite the contrary. The 20mph limits were only put on 30mph roads where the traffic speeds were already 6mph below the limit. That is, because 20mph limits make no significant difference to traffic speeds, they can (or at least could) only be erected where the speeds were already 24mph or less. I thought you would have known that.
Charles, England

Agree (8) | Disagree (5)

From what I understand, info from the Trafic Authorities was that the average 6mph reduction in speed in newly created 20 mph was by the inclusion of other passive measures such at speed humps and cushions etc. The average reduction in speed in 20mph areas without any other means of slowing traffic down other than the signage was only about 1mph. Some 80% plus of light traffic viewed did not comply with the 20mph areas, other measures or not. No suprise there.
R.Craven Blackpool

Agree (5) | Disagree (2)

When assessing 20mph limits, local traffic authorities have usually only been able to afford 20 or 30 points to measure with ATCs (automatic traffic counters). Hence the DfT conducting this research would be expected to provide enhanced information from a larger dataset. However, those who may have an eye for detail rather than headline would find that the total number of ATCs in 20mph roads that this report was based on was 9. Yes I will repeat that 9. See

Hence we should take the statistical significance of these 9 points with perhaps a pinch of salt.

Other detail we know was that all of these were in "free flowing conditions". Of course without the knowledge on the exact locations it is difficult to identify how much the absence of other factors such as people, houses, bends, etc influenced the prevailing speeds. However, if we assume that otherwise they were similar to the 30mph roads chosen then we find some useful information on page 9 of the report. The average speed on the 20mph roads was consistently 6mph or more lower on 20mph roads for ALL classes of vehicle compared to 30mph roads. Hence it would seem reasonable to suggest that whilst not ensuring full compliance, there was a large and useful reduction in speed on 30mph roads when converted to 20mph.

Perhaps the most alarming figure in the report is that 44% of HGVs exceeded the 30mph limit. May I also suggest that as the 20mph reference was to free flowing conditions then the picture of a 20mph zone (probably with speed bumps) does not reflect the actual roads measured.
Rod King, Cheshire, 20's Plenty for Us

Agree (13) | Disagree (7)

Because of the real and major issue of widespread non-compliance clearly highlighted in this article and which I have repeatedly flagged up in other posts, many 'default' 20mph speed limits without engineering measures and enforcement to support them are about as effective and useful as a chocolate fireguard.
Pat, Wales

Agree (16) | Disagree (5)

Surprise, surprise! Surely this report is only confirming what we already know - that unenforced speed limits have little or no influence on driving speeds. Driving speed choice is based on driver perception of the world around them, and unenforced speed limits do little to alter that perception. This fact is reinforced by the report statement that, despite increased recent introductions of lower speed limits all over the country, "average free flow speeds for all vehicle types across each road type have remained ‘broadly stable’". This is why, for me, it beggars belief that there can still be advocates demanding the use of more speed limits to control traffic speeds.

Sure, we all know that slower is safer, but surely we also all know by now, that unenforced speed limits are an ineffective, verging on the useless, and (IMHO) a grossly irresponsible way of trying to deliver slower speeds.
Charles, England

Agree (17) | Disagree (9)

I said recently in a thread on another news story that the urban 30s are the most abused speed limit of the default nationals, but I should have qualified it by saying that the 20s are the most ignored of all speed limits when you include those arising from local orders (the 20s).

Another point, the permanent ATCs are not on the residential roads where the 20s are needed most and some may be legacy counters on main roads which were once 30s but are now 20s and may not be wholly represenative of the speeds on the side roads where as I say, they matter most.

I spent years measuring speeds on roads from 30s to 60s and the stats in the article are about right - the higher the limit the greater compliance usually and is typically where the national limit of 60mph is far higher than the physical characteristics of the road allow anyway.
Hugh Jones

Agree (8) | Disagree (1)