As the pace of innovation in road safety increases and the demand to quickly apply new safety treatments grows, there is no longer time to undertake traditional before-and-after assessment of crashes at trial sites, which can take years to produce results. Increasingly, researchers are looking at surrogate safety measures to understand how effective new road safety countermeasures are in addressing the risk of crashes, especially the more severe crashes, which are even more difficult to study using before-and-after studies.
Surrogate measures, or short-term safety performance metrics/indicators, are now being used in Australasia to evaluate the expected safety outcomes of improvements and help in forecasting future safety benefits. Surrogate measures include operating speeds, traffic conflicts (near misses), change in crash impact angles (e.g. roundabout instead of traffic signals), red light running, levels of jay walking and the number of out of context curves (where there is a big speed change and increased crash risk). Research can be used to demonstrate how a change (reduction) in many of these surrogate measures (e.g. speed) impacts on safety.
A major challenge in the past was the collection of both the before and after data on each surrogate measure. It’s normally too late when the treatment has been applied to do an evaluation using surrogates unless the data required was collected for another reason. Even where the before data was collected, the after data may not be collected as the attention of the team implementing the treatment moves to other projects.
A solution to this challenge is to have a separate evaluation team that manages the project evaluation for each road safety treatment programme. It is important that this team plans what they need to evaluate and what data needs to be collected before and after the proposed treatment is applied, normally across multiple sites or routes. In Victoria, Australia (Safer Roads team), this plan is called an Evaluation Framework.
Whatever the name, it is important that the evaluation plan considers the expected safety objectives of the programme of treatments, the surrogate measures or safety performance metrics that will assess whether these metrics were achieved, and what data needs to be collected before and after the treatments are applied. Often, the evaluation framework will also consider other positive or negative effects expected from the treatment, such as impacts on travel time. The evaluation may also consider the road trauma reduction benefits of the treatment programme, but this will be some years later.
In terms of benefits, evaluation studies of surrogate measures can be used to:
Blog written by Shane Turner, Technical Director, Road Safety