Sandstorm animations on rural expressways: The impact of variable message sign strategies on driver behavior in low visibility conditions

Abstract

Problem: Evolving sandstorms on rural expressways in desert countries impair drivers' contrast vision and increase the risk of serious crashes due to delayed speed adjustments. Intelligent Transport Systems (ITS) such as Variable Message Signs (VMS) conveying warnings can be activated to address drivers’ speed adaptation before entering a low visibility zone. To improve drivers’ understanding of the hazard, a sandstorm animation visualizing turbulent sand and its consequences was designed and compared with a general warning pictogram, which is applied if no specific weather pictogram is available. Moreover, minimum warning distances of the VMS to the low visibility zone were tested (e.g., 300 m or 500 m). Method: Sixty-three participants from the State of Qatar drove in a driving simulator through clear, transition, and low visibility conditions on a rural expressway. A repeated analysis of variances was conducted to examine the impact of the two on-road warning displays on driving behavior. Results: The results showed that the sandstorm animation was similarly effective as a generic warning pictogram in reducing driving speeds before entering the transition and low visibility zone, irrespective of being displayed 500 m or 300 m away. However, the sandstorm animation resulted in consistent similar speed reductions within the low visibility zone, whereas the generic warning pictogram did either perform better or worse after several encounters with a sandstorm. Drivers did strongly agree that the animation is clearly referring to the issue of low visibility, which can be beneficial for recurring low visibility conditions. Practical applications: 1.) Displaying a sandstorm animation is beneficial for rural expressway sections with recurring degrading visibility and low traffic densities, whereas a warning pictogram can be more effective in speed reductions if drivers expect additional traffic hazards. 2.) Roadway authorities have the flexibility to activate a VMS sandstorm warning even for minimum warning distances.