Evaluating road safety schemes: new method raises a new puzzle

Academics are championing a new method to evaluate road safety schemes and predict where interventions will have the biggest impact. But two papers applying the method reach contradictory conclusions.

If road safety measures are installed at sites chosen because of their accident (or casualty) record, evaluating their effectiveness isn’t as straightforward as it may at first seem. As well as having to consider the wider trends in accident/casualty numbers, researchers have to contend with regression to the mean (RTM), whereby an abnormally high collision rate during a monitoring period would be expected to fall even without the road safety intervention being made. 

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