Safety-Based Improvement Measures and Simulation for the Long and Near-Maximum Slope of Expressways in Flat and Rolling Terrains of China

摘要

In the geometry of China's expressway design, due to there being no specific length regulations for near-maximum slope in the Specifications as well as the designers' lack of experience, there are many long and near-maximum slopes (LNMS) on expressways in flat and rolling terrains. LNMS means a longitudinal slope which is under the limited gradient but over the limited slope length, such as where the length of a slope with a 2.9% grade exceeds 900 m. Such places are usually accident black-spots on expressways. In order to analyze the reasons causing accidents on those sections, data are collected at the LNMS sections of the Nanjing-Hangzhou Expressway, which is a typical case. Based on analysis of 5 years' of accident data and on simulation study, this paper presents several effective improvement measures for LNMS of expressways in flat and rolling terrains based on safety considerations. And through VISSM simulation experiment, changes in the operating speed of vehicles are contrasted and analyzed before and after adding the improvement measures. The simulation results show that the safety situation of LNMS is greatly improved after adding the improvement measures, especially setting up climbing lane measures.