The DoT in the UK publishes the following table of stopping speeds in the highway code.
The DoT probably over estimate the distance, but the relative differences at different speeds will be correct.
DoT don’t calculate stopping distances for 15mph. However based on the DoT rules we can work it out, and it’s 7.5m or 25ft.
That means a vehicle travelling at 30mph has an area in front of it 3 times the size of one travelling at 15mph that if a pedestrian enters, they will get hit. The 30mph car is travelling at twice the speed, so that area is swept in half the time. Therefore if a pedestrian randomly steps out into a road of vehicles moving at 30mph they are 1.5 times more likely to get hit than if they step into a road of vehicles moving at 15mph because of the extended braking distance.
An if they do get hit, there is plenty of data on their injury risk.
A comprehensive study by the AAA Foundation in the US measured the likelihood of death and serious injury when a pedestrian is hit at different speeds.
From the their data of 422 pedestrian collisions, the probability of being seriously injured if hit by a car or light truck goes from around 48% at 30mph, to 8% at 15mph; a 6-fold reduction in accident rates.
Coupled with 1.5 times reduction in the probability of being hit in the first place, and a 9-fold reduction in pedestrian serious injuries could be expected by going from a 30mph limit to a 15mph one.
Some pedestrians may be a hit at lower speeds than this – there is no attempt to record the vehicle speed when a pedestrian is hit in the UK. However this paper survey in Sweden found roughly 1/20th the number of pedestrian serious injuries from vehicles hit at 15mph (25km/h) as at 30mph (50km/h).
And if you still don’t believe it, here is a list of links to YouTube uploads of dashcam footage of real pedestrians getting hit at various speeds. We’ve used speedcube to calculate the speed of the vehicle at the moment they impact the pedestrians.
Watch these and then decide for yourself what speed you think drivers should be doing.
Viewers Beware – it’s not for the faint hearted, but if you’re a regular London motorist there is a reasonably high chance that one day you’ll see this through your own windscreen. If you’re a pedestrian, I dearly hope you never see it happen to one of your loved ones.