Pedestrian Fatality Risk and Engine Size

by Adrian Berendt

We often hear that British roads are among the safest in the world.  What we hear less about is that they are no longer getting safer.  The United Kingdom is one of just three countries out of 32 European countries where fatalities rose between 2010 and 2019

Since 2010, the long-term decline in the number of people killed or seriously injured on Britain’s roads has ceased and road casualties are increasing once again.  Particularly shocking is that 10,000 people out walking or cycling were killed or seriously injured in 2018.

We already know the large part played by speed in the probability of a collision and the seriousness of any consequent injury.  We know less about the relationship between injury and vehicle mass. In an article in the Guardian in 2019 two UK researchers – Adam Reynolds and Robin Lovelace – said, “pedestrians [in the UK were] 70% more likely to be killed if they were hit by someone driving a 2.4-litre engine vehicle than a 1.6-litre model.”  We have tested these conclusions for single vehicle / single pedestrian casualties over a five-year period and found broad agreement.  Pedestrians hit by the driver of a car with an engine size larger than 1800cc (1.98% fatal) are 43 per cent more likely to die than if the engine size is less than 1800cc (1.38% fatal).

This risk factor is even higher (50 per cent greater risk of a fatality) for roads with speed limits of 40mph or less.  This is important because eight out of ten pedestrian casualties occur on those roads.

We acknowledge a number of limitations to the research and recommend further research into whether such correlation also holds for serious injuries, whether the ‘engine size correlation’ extends to vehicle mass and size and whether other factors are at play, such as the profile of drivers of particular vehicle types and whether the marketing of such vehicles is linked to particular driving behaviour.

The two principal conclusions from this study are:

1. Pedestrian fatalities and engine size. Reported pedestrian casualties in single vehicle collisions in the UK from 2014 to 2018[1], show a significant positive correlation between the risk of a pedestrian fatality and engine size of the vehicle.  For pedestrians, the chance of being killed when hit by a vehicle with an engine size above 1800cc is 43 per cent greater than that of a vehicle below 1800cc.

2. Speed limits. In relation to speed, the correlation holds for fatalities on roads with speed limits of 40mph or less (where 78 per cent of pedestrian fatalities occur) with the risk from vehicles above 1800cc being 50 per cent greater than that of vehicles below 1800cc.  Above 40mph, the fatality risk for pedestrians is extremely high and there is no correlation with engine size.

The full research report can be downloaded here

[1] The years when the data was readily available and the volumes easily processed

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