Relative fatality risk curve to describe the effect of change in the impact speed on fatality risk of pedestrians struck by a motor vehicle.

Models describing the relation between impact speed and fatality risk for pedestrians struck by a motor vehicle have frequently been used by practitioners and scientists in applying an S curve to visualize the importance of speed for the chance of survival. Recent studies have suggested that these risk curves are biased and do not give representative risk values. These studies present new fatality risk curves that show much lower risks of fatality than before, which has caused confusion and misconceptions about how these new curves should be interpreted, and how this should affect speed management policy. The aim here is to deepen the understanding of the implications this new knowledge has for urban speed policies by analyzing (1) what the most reliable knowledge is for this relation today and what limitations it has, (2) how these risk curves are interpreted today, and what limitations this interpretation has and (3) what the risk curves say about the importance of speed and speed changes. This paper proposes an additional tool, the relative fatality risk curve, to help prevent misconceptions. The proposed relative risk ratios and curves show that, even though the most recent results indicate that the risk is lower than assumed by the older models, the fatality risk is still as sensitive to speed changes as before.