Relationship between Speed and Risk of Fatal Injury: Pedestrians and Car Occupants

The risk of fatality with impact speed (for pedestrians) and change of velocity (for seat-belted car drivers) has been calculated using a logistic regression method, and three current sources of accident data in the UK:

· The On the Spot (OTS) project;

· Police fatal files;

· The Co-operative Crash Injury Study (CCIS).

This same method of logistic regression has been applied to two other important sources of pedestrian accident data: data collected by Ashton and Mackay in Birmingham in the 1970s, and data from the German In-Depth Accident Study (GIDAS) used by Rosén and Sander in their 2009 paper. Using the same method on these different datasets means that the results can be directly compared. The risk of fatality was then plotted in the form of risk curves for each dataset.

Comparison of the pedestrian risk curves from the different datasets shows that the risk of pedestrian fatality is generally higher for the dataset from the 1970s, indicating that the probability of pedestrians being killed when hit by the front of a car has reduced over the last 30 years. In all of the pedestrian datasets, the risk of fatality increases slowly until impact speeds of around 30 mph. Above this speed, risk increases rapidly – the increase is between 3.5 and 5.5 times from 30 mph to 40 mph. Although the risk of pedestrians being killed at 30mph is relatively low, approximately half of pedestrian fatalities occur at this impact speed or below.

Comparing the risk of fatality for a seat-belted driver in a frontal impact with a side impact shows that the risk of fatality is much higher in a side impact than in a frontal impact with the same change of velocity.