Influenced by such factors as road environment and severe weather condition, the probability and severity of traffic accident is much higher on long steep downgrades. This study aims to improve the traffic safety level on long steep downgrades on mountain freeways. First, filed experiments is conducted to collect drivers' physiological data when vehicles travelling on long steep downgrades on typical mountain freeways. The growth rate of heart rate ( GRHR) is selected as the representation indicator of drivers' driving psychology. Then the study develops the relational model between drivers' GRHR and the distance to the beginning of the downgrade, the curvature of current section and the operating speed. Moreover, the traffic safety assessment technique of highway alignment based on the indicator of drivers' heart rate for long steep downgrades is put forward, and the assessment criteria and process is presented. Considering the main traffic safety influencing factors such as the characteristics of road environment and the operation status of vehicles, the proposed model provides theoretical support for the design of highway alignment on long steep downgrades.%山区高速公路连续长大下坡路段受道路条件和不利气候条件影响,发生交通事故的可能性和严重程度均相对较高.本文以提升连续长大下坡路段交通安全水平为出发点,通过典型山区高速公路连续长大下坡路段实车试验,采集驾驶员生理指标数据,并以心率增长率作为表征驾驶员心理变化的指标,建立了驾驶员心率增长率与车辆驶离连续长大下坡路段起点的距离、车辆所在坡段的曲率和车辆运行速度的关系模型；提出了基于驾驶员心率指标的连续长大下坡路段路线安全性评价方法；建立了评价标准和评价流程.本文模型充分考虑了连续长大下坡路段道路环境和车辆行驶特征,可以为山区高速公路路线安全设计提供理论支撑.
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