The risk of a casualty crash doubles (approximately) with each 5km/h increase in travel speed in urban environments, or with each 10km/h increase in speed on higher speed rural roads.
Vehicle travel speeds affect both the chance of crash involvement and the severity of crashes. 

While the setting of speed limits has been the subject of many other Safe System Snippets, it’s clear that driving over the speed limit: 

  • increases your chances of being involved in a crash 
  • means you have less time to react to avoid a crash 
  • takes longer to stop the vehicle to avoid a crash 
  • increases the severity of injury in a crash. 

Research: Travelling Speed and the Risk of Crash Involvement on Rural Roads, Road Accident Research Unit, The University of Adelaide, July 2001 

Video source: TAC