At the end of August, it will be 20 years since the death of Princess Diana in a crash in Paris-our most conspicuous reminder of the frailty of the human body when exposed to the physics of speed.  RoadPeace responded to this tragic loss with a call for drivers to drive at 20 mph. Our parliamentary manifesto earlier that year had called for 20 mph speed limits.

Much has changed in the past two decades. Thanks largely to 20s Plenty for Us who have successfully delivered a people powered /bottom up rebellion, more than half of the largest 40 urban authorities in the UK have 20mph as their default limit.  It is no wonder WHO had them speak at their last road safety meeting with WHO now calling for 30 kph on roads shared by motor vehicles and pedestrians.

And the desirability of this change extends far beyond the immediate concerns of road casualty reduction. The National Institute for Health and Care Excellence (NICE) has endorsed the need for lower speeds both as a means to combat the public health burden of urban air pollution and as a means of promoting active travel.  Reduced speeds are key to the draft (July 2017) Mayor’s Transport Strategy,  based on the Healthy Streets approach, and  reflects this evolution of our understanding of how slower urban speeds are central to a wide range of beneficial outcomes.

It is therefore disappointing (though not entirely surprising) that some people are just not catching on. A recent article in the Evening Standard, by David Williams — who has won awards for his road safety journalism — went out under the headline “Overuse of 20mph limits backfires as most drivers ignore zones”.  It was going wrong from the first photograph, which showed a policeman using a speedgun on motorway traffic.  It’s opening line was “New Department for Transport statistics appear to confirm what many Londoners feared — that the heavy-handed, blanket imposition of 20 mph limits was not only a waste of time and resources — it has backfired.”

The analysis quoted an analysis of free-flow speeds recently published by the DfT. The compliance data did not relate to London, as might have been inferred from the article, but from across the UK, with the 20mph data coming from just nine sites.  Yes, that’s right—only nine 20mph sites from across the nation (it is very unlikely to be more than four or five in London).

The DfT report stated simply that on “30mph roads the average is close to the limit for all vehicle types (28-31mph), while on 20mph roads it is slightly above the limit (21-25mph)” [p. 1].  There was never any doubt that speeds on 20mph roads were lower than on 30 mph roads.

In the article, the “evidence” for the 20 mph policy has “backfired” came not from the DfT but from a quotation from someone at IAM RoadSmart, an organisation that developed its policy position on 20 mph limits through a survey of the attitudes of 1001 drivers.

The IAM survey results were certainly more equivocal than the conclusions that they reached. The responding motorists were divided in their views, with more than 30% being in favour of a shift to 20 mph limits. And between 70%-80% in all age groups recognised the benefits that 20 mph would bring to pedestrian safety.  But the key point is that motorists are not the only road users: in London more journey stages are completed by pedestrians than motorists. And for pedestrians there is a lot more at stake, as the fraction of motorists that do break the limit are much more dangerous in a 30 mph zone, due to the rapid rise in the risk of fatality in a collision above this speed.

Basing recommendations for public policy on the views of a small majority of a minority group is poor practice. Moreover, disguising what was clearly nothing more than an opinion piece as fact based journalism is poor practice – fake news, to coin a phrase.

And this fake news is dangerous. In the article itself, the author points to the link between perceived legitimacy and compliance.  We can’t know how many drivers reading the article concluded that it sanctioned their past (or future) disrespect for these limits.  But we can worry.

Updated on: 20 July 2017