Advantages and disadvantages of reactive (black spot) and proactive (road rating) approaches to road safety engineering treatments – when should each be used

A fully funded safe systems approach entails roads being treated with barriers, pedestrian bridges, etc. as well as appropriate speed management to avoid road users being exposed to intolerable physical forces in crashes. The practical reality for most developed as well as low and middle income countries, is that this will not occur for some years. In the interim, we must select works and locations which provide the best road safety gains from limited resources. Significant controversy remains as to how to do this best, with the debate polarising around two alternatives: the reactive or black spots approach based on known crash history versus the proactive approach based on engineering deficiencies identified by various means of audit and road ratings. This paper presents a review of evidence and process analysis to comment on the advantages and disadvantages of each approach. The polarisation of the debate has led to absolutist answers of one option being always superior. The reactive approach works well only if reliable data on crash type, location and severity exist; it has the advantage of accommodating variation of crash history which may depend on non-engineering factors such as being several hours from a major city causing greater fatigue risk or proximity to hotels adding to drink-driving risk. Road assessments have the advantage of not relying on reliable crash data, which for many countries do not exist, and are the only option for new or re-engineered roads. Road assessments are currently more intimately connected to safe systems principles, although it is not clear that this is an inherent rather than historical advantage. This paper suggests that there are circumstances in which each approach is superior, and recommends a decision process for determining which to employ, in addition to consideration of a combined approach.