Having been invented by Nobel Prize winning physicist Arthur Holly Compton in 1953, speed bumps were quickly adopted around the world’s cities as a form of traffic calming, largely unquestioned. Forcing motorists to slow down in areas with higher risks of car-to-car or car-to-pedestrian collisions, the simple device is has recently been the subject of academic research at the U.K.’s University of York and Imperial College London’s Center for Transportation Studies. The conclusion? Cities should remove speed bumps close to schools and playgrounds – where they are in fact most often placed – to limit the direct exposure of children to increased pollution.
Professor Alastair Lewis, Professor of Atmospheric Chemistry at the University of York, explains to The Telegraph that his team’s research has proven that forcing drivers to slow down and speed up again in a short distance increases air pollution: when a car slows down to approach a speed bump, the friction caused on the brake pads and tires, when it speeds up again after descending the bump, there is a sharp increase in exhaust emissions.
“There is a road safety benefit to road humps, but they were not introduced with air quality in mind. They almost certainly reduce air quality. The constant breaking and accelerating required to go over road humps would not seem the best method of traffic calming to use outside schools,” explains Professor Lewis.
Comparing routes with traditional speed bumps, that extend the whole width of a street, to those with speed cushions, which are centered and thus don’t require drivers to break as sharply, the Imperial College London research saw a huge difference in pollutant levels. In one London street, fitted with traditional speed bumps, a petrol car released 64% more Nitrogen Dioxide (NO2) than in a similar street with speed cushions. It also produced 47% more Particulate Matter (PM) and nearly 60% more Carbon Monoxide (CO2) emissions.
Their findings were even more pronounced in diesel-powered cars which produced 98% more NO2 when driven over bumps rather than cushions, as well as 64% more CO2 and 47% more PM.
“On the acceleration cycle you get combustion pollutants. On the braking part of the cycle you get non-exhaust emissions caused by friction on brake pads and tires which throws out fine particles into the air – this happens even if you drive an electric car,” says Professor Lewis.
“We have a public health emergency in many countries. Urban air pollution continues to rise at an alarming rate, wreaking havoc on human health. It’s dramatic, one of the biggest problems we are facing globally, with terrible future costs to society,” said Dr Maria Neira, director of public health at the WHO in Geneva, earlier this year. Alarmingly yet, outdoor air pollution contributes to over 3 million deaths a year.