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Reducing injury from speed related road crashes
  1. I Johnston
  1. Correspondence to:
 Professor Ian Johnston
 Monash University Accident Research Centre (MUARC), Building 70, Monash University, Victoria 3800, Australia;

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Towards the achievement of a population based preventive strategy

While speed management is a key element in the road safety strategies of many regional and national governments, there is little consensus and much controversy over the specific speed reduction interventions that have been employed. Considerable heat—and relatively little light—has accompanied the public debates.

This paper reviews the evidence for a population based speed reduction strategy, based predominantly on the widespread mismatch between extant speed limits and levels of infrastructure safety. It then explores how jurisdictions have inflamed public opposition to their interventions with flawed public policy decision making and concludes, hopefully, by putting the baby firmly back in the bath.


There can be no doubt that decreasing vehicle travel speeds reduces stopping distances and impact speeds, and thus the incidence of serious casualties and fatalities. While individual studies can be criticised, the weight of evidence, both within and across methodological paradigms, is overwhelming:

  1. Numerous studies, across many countries, have evaluated the injury outcomes of changes in prevailing speed limits, both urban and rural. Almost invariably, fatalities and serious casualties have fallen when speed limits have been lowered and have increased when speed limits have been raised.1,2 On interstate highways in the United States, for example, the limit was reduced in the 1970s, restored to its original level in the late 1980s then further increased, in numerous states, in the mid to late 1990s. Fatalities fell, rose, and then rose again correspondingly.3,4 Such is the consistency of results from these types of study that some writers have posited predictive relationships between shifts in speed distribution and crash injury outcomes.

  2. Case-control studies, of which there are few, show that both the probability of involvement in a casualty crash and the severity of injury when a crash occurs increase …

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