Advanced Driver Assistance Systems may contribute to making driving safer, road use more efficient and the trip more comfortable. For the human-centred development of these systems, understanding driving behaviour both in normal circumstances and in reaction to unexpected, safety-critical situations is crucial. The thesis focuses on drivers’ reactions to unexpected situations in an urban environment and the effects of event urgency and mental workload. Two large driving simulator experiments were conducted, consisting of many consecutive urban intersections that were similar with respect to layout and road user behaviour. The setup suggested that all intersections were similar. However, after these expectations had been established, drivers were confronted with an unexpected and safety-critical event, such as a suddenly breaking lead vehicle. Participants’ mental workload was increased for certain groups during parts of the experiment using a serial subtraction task. Drivers showed reduced attention to driving in a dual-task situation, resulting in an automatic, habitual driving style and being less responsive to mildly urgent situations. Drivers with increased mental workload only changed their driving style when the situation was highly safety-critical, and their cautionary response lasted shorter than in normal drivers. However, the effect of the most safety-critical event was stronger in mentally loaded drivers than in regular drivers. While drivers with an easy subtraction task generally performed well on this task, they drove less cautiously than non-loaded drivers. Conversely, highly loaded drivers made many mistakes on a difficult subtraction task but simultaneously drove more cautiously. This indicates that drivers prioritize safe driving over secondary task performance when the combined task demands are too difficult to handle. However, since their primary task performance was nevertheless affected, conducting a secondary task (such as using a mobile phone) may have severe consequences for safe driving. The results are related to the hierarchical model of the driving task (Michon, 1971, 1985). The model’s premise that top-down interaction between task levels turns into bottom-up interaction in unexpected situations is partly confirmed. However, the effect of specific types of events can not be predicted with the model in its current state. Some additions to the model, related to event urgency and mental workload, are suggested.
|Award date||2 Feb 2012|
|Place of Publication||Enschede/ Delft|
|Publication status||Published - 2 Feb 2012|