Safe speed limits for a safe system: The relationship between speed limit and fatal crash rate for different crash types

<p><b>Objective</b> To provide empirical evidence for ‘safe’ speed limits that will meet the objectives of the Safe System by examining the relationship between speed limit and injury severity for different crash types, using police-reported crash data.</p> <p><b>Method</b> Police reported crashes from two Australian jurisdictions were used to calculate a fatal crash rate by speed limit and crash type. Example ‘safe’ speed limits were defined using threshold risk levels.</p> <p><b>Results</b> A positive exponential relationship between speed limit and fatality rate was found. For an example fatality rate threshold of 1 in 100 crashes it was found that ‘safe’ speed limits are: 40 km/h for pedestrian crashes, 50 km/h for head on crashes, 60 km/h for hit fixed object crashes, 80 km/h for right angle, right turn and left road / rollover crashes, and 110 km/h or more for rear end crashes.</p> <p><b>Conclusions</b> The positive exponential relationship between speed limit and fatal crash rate is consistent with prior research into speed and crash risk. The results indicate that speed zones of 100 km/h or more only meet the objectives of the Safe System, with regard to fatal crashes, where all crash types except rear end crashes are exceedingly rare, such as on a high standard restricted access highway with a safe roadside design.</p>