Safer Speeds – The Real Data

I have commented before on how Transport for London (TfL) have failed to justify their “Safer Speeds” proposals which includes imposing 20 mph speed limits on many roads. We have previously pointed out how TfL have been misinterpreting police accident data to support their claims that the measures are justified.

For example, they issued a Tweet that said “speed accounts for 37% of all death and serious injuries” in road accidents in London. That figure is simply wrong. The claim was allegedly based on the STATS19 data reported by the police (a form they fill out about every accident involving injuries).  That form allows for multiple factors to be recorded and after submitting a Freedom of Information Act request we learned that they counted all the accidents where factors 306, 307 and 602 were noted.

But factor 602 is described as “Driver/rider either behaved in a negligent or thoughtless manner or was in a hurry….”. Clearly the key word in that sentence is the second “or” when TfL have interpreted it to mean “and”.  There is no basis for claiming that all accidents where factor 602 is attached were rated by the police as ones where a driver was in a hurry. They might have simply been careless. Only where the other factors 306 or 307 were also noted could there be any claim that speed was a factor in the accident.

We now have the complete accident data and the data makes it plain that exceeding the speed limit (factor 306) is a very minor factor in KSIs (Killed and Serious Injuries) in London. It’s actually recorded as a contributory factor in only 5.9% of such accidents in the last five years. That’s actually less than the figure of 7.1% reported by the Department for Transport for the national figures in 2018 – see table below. Clearly tougher enforcement of speed limits is therefore unlikely to have much impact on the overall numbers. That of course is particularly so in London where average traffic speed is typically well below the speed limit.

Contributory Factors and Speed - ras50008

The largest contributory factor by far is “Failed to Look Properly” which accounted for 42% of KSIs in London or 35% nationally. But there are several other factors with higher ratings than “Exceeding the Speed Limit” such as “Poor Turn or Manoeuvre”, “Failed to Judge Other Persons Path…”, “Loss of Control” and “Careless, Reckless or in a Hurry”.

Even if you bundle factors 306 and 307 together only 12% of KSI incidents are included nationally so reducing speed limits is going to have only a small contribution at best to reducing such accidents. It’s reducing the other factors that is the key to substantially reducing road casualties. More driver education, improved roads and research into saccadic masking may be productive.

Note also that a lot of the reported factor 306 and 307 claims of excessive speed and speed above the speed limit might well involve illegal use of vehicles such as stolen vehicles so reducing speed limits will have negligible impact in reality.

There is simply no cost/benefit justification for the Safer Speeds proposals as pointed out in our previous article and TfL have clearly been abusing the data so as to make spurious claims.

Roger Lawson


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Mayor’s Vision Zero Strategy Failing

In 2018 the Mayor of London launched the Vision Zero strategy to reduce road casualties in the capital city. But road casualty figures for 2018 show that Killed and Seriously Injured (KSIs) on London’s road actually increased by 5% to 4,065 in 2018. Vision Zero is a key part of Mayor Sadiq Khan’s Transport Strategy along with the encouragement for modal shift with the aim of getting more people walking and cycling.

However, cyclist fatalities actually rose by 20% to 12, and cyclist serious injuries rose by 14% to 770. Cycling is one of the most dangerous ways to travel so is this encouragement to cycling misconceived?

The trend in London KSIs matches the national picture where road deaths have plateaued in recent years. See chart below from the DfT report of national road casualties in 2018.

National Fatalities 2018

We will no doubt see renewed calls for lower speed limits and more enforcement, but the ABD has consistently argued that the focus on simplistic solutions to road safety problems, such as traffic speed reductions, cannot and will not work to cut the horrendous toll of road casualties. The encouragement of cycling is surely an example of an unintended consequence of a policy introduced with the best of intentions to improve the health of the population. In London enormous expenditure on Cycle Superhighways and cycle lanes of other kinds has been incurred in the last few years. This was justified on improving cycle safety but in reality the impact is not apparent. The encouragement of cycling may have actually made the road casualty statistics worse.

The ABD has argued that Vision Zero is a counter-productive road safety fantasy. We argue that more attention should be paid to road user education and road engineering. See our submission to Parliament’s Road Safety Transport Committee in April 2019 given below:

Evidence to Transport Committee 2019: Evidence to Transport Committee 2019-03-26

London Road Casualties 2018:

National Road Casualties 2018:

Postscript: With the appointment of Andrew Gilligan as a transport advisor to our new Prime Minister Boris Johnson, who as former London Cycling Commissioner under Boris was a big contributor to the growth of cycling in the capital and what many argue is the wasted expenditure on Cycle Superhighways, will we see the same defective policies being spread across the country?

Roger Lawson


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Speed Humps and Air Pollution

Air pollution from motor vehicles, particularly in major conurbations such as London, has been a hot topic of late. The impact may be exaggerated but it has certainly become a matter of public concern with the increase in diesel vehicles allegedly making it worse.

It has been known for many years that speed humps actually result in more air pollution. For example this writer published an article back in 2002 which said the following: “Pollution Caused by Traffic Calming. As a contribution to the local debate on the merits of speed bumps, it is worth covering a report produced by the  TRL (Transport Research Lab.) last year. In the past, different studies in different countries seemed to produce very diverse results, but the latest methodology seems more likely to have produced accurate figures. TRL Report No. 482 studies the effect of a number of different traffic calming measures, including road humps, cushions, pinch points and mini-roundabouts. They also studied the impact on traffic flows and delays experienced by fire engines. To quote from the report “The results of the study clearly indicate that traffic calming measures increase the emissions of some pollutants from passenger cars. For petrol non-catalyst, petrol catalyst and diesel cars, mean emissions of CO per vehicle-km increased by 34%, 59% and 39% respectively. For all three vehicle categories the increase in mean HC emissions was close to 50%. Emissions of NOX from petrol vehicles increased only slightly, but such emissions from diesel vehicles increased by around 30%. Emissions of CO2 from each of the three vehicle categories increased by between 20% and 26%. Emissions of particulate matter from the diesel vehicles increased by 30%.

The advocates of speed humps ignored this negative evidence in their commitment to road safety even though their impact on accidents is very marginal and may be a mirage.

As confirmation for the above a recent study from Imperial College, London also found high levels of pollution from road humps – indeed higher than from other forms of traffic calming (see the Daily Telegraph on the 11/6/2016 for a fuller report on this and some quotes from me).

For example they got 47% more particulates and 64% more NO2 from a petrol car when driven over humps, and even higher figures for diesel cars.

As I pointed out in my comments to the Daily Telegraph, accidents to school children are not particularly frequent outside schools so putting humps there is unnecessary. But the health impact on children of air pollution may be particularly severe. There are numerous reasons why the use of speed humps should be banned and this is yet another – see this page for lots more information written by the author on this topic some years ago (and the facts have not changed since):

Roger Lawson