Mechanics of the passing maneuver and the impact of large trucks

Many highway agencies are evaluating the impacts of long combination vehciles on two-lane freeway operations. A critical element of this evaluation is the impact of the large trucks on the passing sight distances required for safe overtakes. This paper reviews recent analyses of the passing maneuver and highlights a number of inconsistencies in these approaches. The paper then introduces a modified model that better reflects the characteristics of the passing maneuver and illustrates the effects of different assumptions about acceleration, deceleration, and vehicle clearances on passing sight distance requirements. The paper concludes with some passing sight distance recommendations for different design speeds and overtaken vehicle lengths. The introduction of long combination vehciles on two-lane roads would increase passing sight distances for design and marking by substantial amounts.