Study On The Safety Assessment Of Vertical Design In Expressways

The safety of road users is determined by traffic safety. Meanwhile, safe and smoothhighways, especially expressways, which are considered to be the main artery of highwaytraffic, have a great influence on the development of national economy. In highwayalignment design, vertical design is so important that poor design could always lead toaccidents. According to statistical data, more than40%of accidents happened onexpressways are related to unreasonable vertical design. In consideration of thecharacteristics of expressways and the significance of longitudinal safety issues, thisdissertation studied the mechanism of accidents which happened on the longitudinal slopesections of expressways. Then, a safety assessment method for such sections is proposed.The purpose of this dissertation is to provide theoretical basis and technical support formanagement decisions during the design and operation stage of expressways.This dissertation analyzed the characteristics of accidents happened on longitudinalslope sections and summarized the distribution law of accidents from four aspects, whichare vehicle type, distribution of time, accident forms and causes. Next, the causes of uphillaccidents and downhill accidents were analyzed separately in order to find out theinfluencing factors longitudinal safety, including alignment indexes and traffic conditions.Then, the purpose, function and principle of safety assessment is introduced briefly. Inaddition, indexes of safety assessment (including longitudinal grade, radius of vertical curve,mix rate of large vehicle, speed reduction of lorries on longitudinal slopes, temperature ofbrake rim on downhill sections, speed disparity between passenger cars and lorries ondownhill sections, etc.) were put forward based on the analysis done previously, and theevaluation criteria was established. Afterwards, the assessment methods were proposedusing a nonlinear fuzzy synthetic evaluation model. Finally, the evaluation method was usedto assess the safety level of typical sections on Chaohui Expressway.