2023 - NZ - Role of Speed in Serious Crash Injury

Multiple sources of evidence address the contribution of speed and speeding in crashes: police crash reports, in-depth crash investigations, studies of speed and serious crash risk, assessments of survival and injury rates for various impact speeds, and evaluations of the safety outcomes of speed management interventions. These sources of evidence all indicate that speed is a major factor in crash trauma, but appear to differ in estimates of the extent of the role of speed. This paper employs New Zealand as a country case study, undertaking a targeted assessment of data from the different sources to better determine the roles of speed and speeding in serious crashes. We find that apparent mismatches of estimates of the role of speed from different sources largely arise for two reasons. First, the studies vary in methodology and thus validity, and second the data from the different sources provide answers to fundamentally different questions, which are then incorrectly subsumed into the general question of the role of speed. Finally, we answer the question: ‘What is the extent of the role of speed in crashes, and particularly deaths and serious injuries?’ by providing answers to the different ways of couching these questions. Depending on the question, correct answers range from 20% to 100% of serious crashes. By combining evidence from different sources, we estimate that speeding is involved in around 60% of fatal crashes in New Zealand, and that speeds above New Zealand’s Safe and Appropriate Speeds are involved in around 71% of injury crashes.