Speed Impact Tool

Speed plays a significant role in road safety outcomes. Even small changes in average speeds can have a big impact. Through substantial research, models have been developed that provide guidance on the estimated impact from a change in speed. Early research led to Nilsson’s “Power Model” which identified that a 1% increase in average speed results in approximately a 2% increase in injury crash frequency, a 3% increase in severe crash frequency, and a 4% increase in fatal crash frequency. Reductions in speed lead to equally substantive reductions in deaths and injuries.

More recent research has led to refinements in these models, with the most recent iteration being developed by Rune Elvik and colleagues based on an Exponential Model. This model has now been embedded in a tool that can be downloaded and used by practitioners and decision makers around the world. This basic tool provides estimate on the change in fatal and serious injuries from either an increase or decrease in speed.

Usage instructions are provided within the tool. Like any model, the tool has limitations, including that it has been derived from research in high income countries, and in limited environments. Please read the limitations carefully before using the tool.

Many people do not realize the impact that even small changes can have on safety outcomes, so we hope that this tool will be useful when engaging on discussions around change in speed. Please let us know what you think about this tool.