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): http://www.bromleytransport.org.uk/Humps.htm

Roger Lawson

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