Effect of road geometry on driver fatigue in monotonous environments: A simulator study

Driver fatigue, induced by task monotony can increase the risk of road accidents. Highways are usually designed with few geometric changes so that high-speed traveling would be possible. Such conditions when combined with repetitive and stimulus-free environments, create a monotonous driving experience that can lead to mind wandering and task disengagement, and subsequently affect driver's performance. This paper focuses on the relationship between road geometry and driver's vigilance level in monotonous environments. Therefore a driving simulator experiment with three different scenarios, which were originated from three existing highways in rural areas of Iran, with low, moderate, and high levels of geometric variety was developed. Participants drove for 45 min in each scenario and their steering wheel movements (SWM), standard deviation of steering wheel movements (SDSWM), and lane positioning ability (indexed by the area between trajectory and road's centerline (ABTC)) was analyzed. The results indicated a significant effect of road design on lane positioning (P < .001). The mean value of total ABTCs showed 11.3 and 20.6 percent of performance improvement for scenarios with moderate and high geometric variety respectively. Also, a significant effect of time on task was observed on SWM and SDSWM (P < .001). However, the deterioration rate was considerably lower in scenarios with higher geometric variety. This work can help to develop more efficient monotony countermeasures with regards to road's geometric design characteristics. It also provides useful information for more optimized road designs in such environments from driver's mental workload perspective.