Driver fatigue is estimated to be a (contributing) factor in 15 to 20% of crashes, but estimates in individual studies vary widely. Drivers who are tired are less attentive and react less quickly and less adequately than drivers who are not tired. They also get irritated and frustrated more easily.

Sustainable Road Safety implies that the traffic environment is designed to rule out serious crashes and to mitigate the severity of the crashes that do happen. The human dimension is the primary focus: man who is vulnerable, makes mistakes and does not abide by the rules.