摘要:AbstractThis paper analyses the clear zone design parameters, including driver reaction time, conditions of vehicle leaving roadway and driving distance in clear zone. Meanwhile, in classical physics, the process that the vehicle runs off roadway can be seen as a combination of uniform motion in a straight line and rectilinear motion of uniform deceleration. Then, based on the forgiving design concept, the paper sets up a calculation model for the roadside clear zone. It calculates width range of roadside clear zone. According to the calculated results and the actual instance of roadside, it brings forward the recommended width of roadside clear zone. Compared with RISER (Roadside Infrastructure for Safer European Roads), the paper considers driver reaction time, so the calculation of clear zone width is larger and safer. However, the computed results are reasonable and acceptable because they are essentially consistent with the suggested clear zone distance in AASHTO's Roadside Design Guide (American Association of State Highway and Transportation Officials). Therefore, the research results of the paper could be a supplementary guidance or reference for road designer and administrator.