OPERATIONAL AND SAFETY PROBLEMS OF TRUCKS IN NO-PASSING ZONES ON TWO-LANE RURAL HIGHWAYS

Two-lane rural roads in mountainous terrain with large truck volumes pose a real problem for the motorist. Extended roadway sections with severe sight restrictions and inadequate passing opportunities can make overtaking and passing a slow-moving vehicle extremely difficult. Further, the ability of large trucks to maintain speed decreases drastically over lengthy gradient sections. The inability of motorists to pass slower moving vehicles on these highways causes reductions in throughput and increases in delay, conflict, and hazard. Passing maneuvers on two-lane highways require a series of complex information-processing and decision skills, which makes these maneuvers one of the most demanding and risky operations performed by the motorist. Trucks require considerably longer distances than do automobiles to pass on two-lane rural roads. Even with their greater eye heights, truckers are placed at a disadvantage under the current system of marking no-passing barriers. The purpose of this paper is to discuss the interactive effects of geometric design elements and traffic composition (with particular emphasis on truck traffic) on traffic accidents and operational aspects on two-lane highways in mountains. Included in this analysis are passing-related accidents, human factors elements, and the impact of passing lanes and four-lane sections. Conclusions and recommendations, which draw on the findings of various research studies on the topics of truck traffic and no-passing zones, are also presented.