Background The words “complexity” and” complex system are increasingly used in road safety and transport system literature. They refer to the acknowledgement of the complexity of the multi-causal nature of road safety issues, and their solutions. The terms have also been used in describing the complexity of changing individual behaviours or policies, anticipating and assessing the consequences of interventions. Hence, it seems rational turning to complexity science for insights.

Description of the problem Complexity science is about complex adaptive systems (CAS). It defines a complex adaptive system as a collection of autonomous, interactive and adaptive agents that act freely in diverse ways, and are unpredictable and, non-linear but interconnected. It is considered an ever changing system, typically with fuzzy boundaries which is built of multi-layer nested systems.

Changes Utilising the lenses of complexity, a road traffic system is perceived as a dynamic complex adaptive system formed of many diverse interdependent agents including individuals, culture, environment, policies, vehicles and roads which constantly change. In addition, any change in one aspect or component of this system can significantly change other parts and so the whole system. This new understandings provides new explanations for current road safety issues leading us to new understanding of potential adaptable solutions.

Conclusions This paper will explain this new understanding. By doing this, it suggests that utilising concepts of complexity science is a promising line of inquiry to explore successful approaches to context and time dependent road safety interventions. It also argues that it is not possible to remove the complexity, but we need to harness it in order to be able to develop more safe transport systems across all countries and communities.