“Changing social norms is vital for 20 mph success”

The following letter under this title appeared in Local Transport Today 769 (29 March – 11April 2019).I wonder if I could raise two issues in the ongoing debate about 20 mph and your Editorial (LTT 768) which have not attracted much, if any, attention?

Firstly, there is confusion between numbers reported as casualties in Road Traffic Collisions and safety. As we have been saying in the Road Danger Reduction movement for decades, the two are different and may even be inversely related. (See my Viewpoint in LTT 635 for a simple explanation of this). There is certainly a place for good quality analysis of the casualty figures – but this has to be placed in the context of how we fully define “safety”.

Secondly, a key question has been the discussion around motorists’ speed. Debate has existed since 20 mph areas and/or zones were rolled out as to what effect they would have: would engineering methods be required to get speeds below 20 mph? Would there have to be heavy traffic calming or could we get away with minor treatments like some alteration to median marking? How about some policing, such as is currently done by West Midlands Police Road Harm Reduction Team? Should we rely on fixed cameras (concealed or otherwise) or do we have to go straight on to automatic on-board speed governors?

The idea of 20 mph as a maximum speed for motor vehicles in areas with significant pedestrian traffic has been around for a while. It’s commonplace in parts of Europe such as northern Germany (not exactly a country hostile to the private car!) and was advocated 50 years ago in this country by Buchanan despite his advocacy of a car-centred urban transport system. Driving below 20 mph rather than below 30 mph increases time to react and cuts the potential kinetic energy dispersed on impact, with particular relevance to pedestrian and cyclist safety, and we have known this for some time.

As few commentators (with the exception of such as Ben Goldacre) have pointed out, the issue here is this: a large proportion of drivers (generally the majority) in 20 mph areas simply do not want to obey the law. That’s the bottom line here: if we want a more civilised highway environment it has to be socially unacceptable to use a motor vehicle going over 20 mph on roads with actual or potential significant concentrations of people walking or cycling. Arguing about exactly how to get there is a secondary issue.


Dr Robert Davis, Chair, Road Danger Reduction Forum

2 thoughts on ““Changing social norms is vital for 20 mph success”

  1. Pingback: “Changing social norms is vital for 20 mph success” | Road Danger Reduction Forum

  2. Mike Chalkley

    Areas and roads are usually made 20mph where there is arterial traffic. The solution is to use filtered permeability to reduce both traffic speed and volume.


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