You are here
Articles in Taxonomy
Areas of Expertise (2)>>
Core Tasks (1)>>
Each road traffic “participant” is liable to be involved in an accident. Various factors play a role in this risk. Accidents are very rarely the result of a single unsafe action; they generally imply a chain of circumstances and events that may lead to an accident-prone situation. The following diagram (known as the Swiss Cheese Model) suggests that various types of error (“latent errors” and “unsafe actions”) must be present at the same time to cause an accident.
Diagram illustrating the causation of an accident by latent errors and unsafe actions
(Reason, J. (1990). Human Error. Cambridge, Cambridge University Press
Reproduced in CROW (2009). Road Safety Manual. CROW Record 26).
So the causes of road accidents are multiple and often find their source in a cocktail of events that can be related to one of the three components of the safety triangle – the user, his vehicle (or his travel mode), and the infrastructure he uses – or a combination thereof. According to several studies1 only 2 to 3 % of all accidents are caused by the road environment or the road infrastructure (alone). However, when combined with the other two factors (the user and his vehicle) the infrastructure plays a role in 18 to 34 % of accidents.
This finding obviously argues in favour of actively implicating the infrastructure in efforts to improve the safety of the road transport system, all the more as (intelligent) infrastructural measures often rapidly have a durable effect.
In concrete terms, the layout of a road can contribute to better safety in various ways:
 Treat, J. & al (1979). Tri-Level Study of the Causes of Traffic Accidents, 1979, Washington DC – Cited in PIARC (2003). “Road safety manual”.
Hillier, P. 2002. “Highways liability and the investigation of road traffic accidents”. Paper at: IPWEA NSW Division Annual Conference 2002. TRL.