Speed bumps

There has been a large discussion around speed bumps over the past few weeks, since Environment Secretary Michael Gove announced that councils should consider removing them as part of a drive to improve air quality.

This comes after research suggests that speed bumps double emissions of harmful fumes by causing vehicles to repeatedly slow down and speed up.

However, we are urging local authorities to consider very carefully the implications of completely removing any speed bumps.

RoSPA strongly supports the use of 20mph zones – where speed bumps and other such measures would be used to regulate the speed of vehicles – as they are an effective means of reducing the number of road crashes, deaths and injuries.

The majority of pedestrian casualties occur in built-up areas, with 20 of the 25 children and 288 of the 383 adults who were killed in 2015 dying on built-up roads. Yet studies have proved the effectiveness of 20mph zones: a major review of zones in London by the BMJ demonstrated that casualties were reduced by over 40 per cent, with fatal or serious injuries to children being reduced by half.

And there are other benefits, too. Not only is the accident rate reduced, but those hit by a car at 20mph are much less likely to be killed or seriously injured. 20mph zones also increase rates of cycling and walking, which of course produce zero harmful emissions.

So, RoSPA does not want to see the wholesale removal of speed bumps. However, councils may wish to replace bumps with speed cushions, which, a study by Imperial College London has shown, cause cars to produce less nitrogen dioxide due to their narrower and shallower nature. This may also be the case for areas where councils are considering introducing new zones.

A 2017 article by Public Health Wales staff has also suggested that if all 30mph limits in Wales became 20mph, six to 10 lives would be saved and 1,200 to 2,000 casualties avoided each year (roads with 20mph limits, rather than zones, are usually those without traffic calming measures).

There is also a part for drivers to play.

The increased emissions are caused when cars speed up and slow down in between bumps. Of course, this would be mitigated if drivers were to stay at the same speed throughout a 20mph zone, i.e. not speed up between bumps.

Finally, it’s worth remembering that speed bumps have been put down historically where there has been a history of collisions involving vulnerable road users. If speed bumps are removed to improve air quality, it is essential that this does not endanger those living and working in the area. It should not be either/or. With imaginative street design, we should be able to improve air quality while maintaining safety on our roads.

For more information on 20mph zones and limits, see our dedicated webpage and factsheet.

Nick Lloyd, road safety manager