In this study subjects kept diaries about unintentional acts during driving. They were asked to record errors at skill-based level: slips and lapses. They also recorded the circumstances preceding these errors and the consequences for road safety. It was demonstrated how insight into the nature and antecedents of these 'human errors' contributes considerably to the understanding of road safety. By focusing on the conditions which control the occurrence of unintentional acts the study shows how these errors or their consequences can be controlled. A relationship was established between the specific conditions that evoke these slips and generic classes of condition that are conducive to errors: latent failure types. It is argued that in conditions controlled by latent failures cognitive processes produce not only skill-based errors but also rule- and knowledge-based errors. It is claimed that strategies to increase safety should be directed at these latent failures, rather than at the errors that follow from them.
