Evaluating the effect of vegetation and clear zone width on driver behavior using a driving simulator

•Twenty-three drivers participated in a driving simulator study.•Clear zone width and roadside vegetation density varied throughout the drive.•Participants drove slower in small clear zones than large clear zones.•Participants moved their vehicle closer to the centerline in small clear zones.•The density of roadside vegetation did not affect speeds or lateral positioning. Roadside vegetation provides a myriad of environmental and psychological benefits to drivers. While research has shown that natural landscapes cause less stress and frustration to the driver among other benefits, the same vegetation may potentially increase the severity of run-off-the-road crashes. The aim of this study was to evaluate the extent to which clear zone width and roadside vegetation density influence operating speeds and lateral positioning to determine whether the roadside environment has any effect on drivers’ attention to their speed. A within subject driving simulator experiment tested six combinations of clear zone widths and roadside vegetation densities. Participants’ driving performance was measured throughout the virtual drive. Along tangents and curves to the left, participants slowed down and drove closer to the centerline when trees were near the edge of the road. Similar to the results reported in Calvi (2015), no statistically significant differences in operating speeds were observed with change in vegetation density. The analysis of drivers’ eye movements indicated that the roadside configuration did not affect participants’ attention to their operating speed, however, the number of glances was highly correlated to the time spent in the virtual drive. The results provide evidence to suggest that, while the increased roadside vegetation density does not necessarily result in reduced driver speeds or deviated lateral positioning, the manipulation of the roadside clear zone width does provide tangible benefits to safe driver behavior. These research findings should be considered in the design of roadside elements, accounting for overstated benefits to roadside vegetation.