Before-and-after studies using crash data and iRAP protocols

This report shows that evaluation of any work is important because it demonstrates how effective that activity has been.

There are many ways to evaluate improvements to road infrastructure to check that they are reducing risk. It is possible to monitor safety at particular locations or over networks as a whole.

Over a long period of time, it is possible to check if the number of crashes has reduced at locations where infrastructure has been changed. A “before-and-after” methodology using crash data is described here. iRAP’s Risk Rate Mapping and Performance Tracking can also show before-and-after changes in risk and these techniques are illustrated here.

Where good crash data do not exist, it is necessary to measure risk indirectly, often by monitoring intermediate measures that are known to increase or decrease the risk of injury. The iRAP Star Rating is one such measure. Examples are shown of improvements in the safety of a road measured by the Star Rating.