The Effect of Shoulder Width on the Heavy Vehicle Driver's Behavior in the Two Lane Rural Roads by Using Driving Simulator

Safety of vehicles in traffic is one of the most basic principles of traffic engineering and transportation planning in the world. Roadway design is one of the most significant factors that affect driving behavior and safety. In this study the effect of combination of three roadway design elements – shoulders width, guardrail existence and roadway geometry (curvature) – on the behavior of heavy vehicles drivers in the two lane roads was evaluated using bus driving simulation (BI 301 FULL). Six scenarios were designed to investigate the effects of these three elements. Forty heavy vehicles drivers participated in an experiment with a driving simulation in designed scenarios. In the case of existence of guardrails, the shoulder width have a specific effect on speed and distance to the midline. The beneficial effect of shoulder width on driver behavior greatly reduces in the absence of guardrails. The rate of changes in speed and distance from the midline with the changes in shoulder width is lower in the night than the daylight due to low speed and high workload in the night. Roadway geometry can be used to decrease speed. The results also revealed controlling the width of road shoulders and placing guardrails is a safe way to control speed and lane position.