RELATIONSHIP BETWEEN ALTITUDE AND OPERATING SPEED IN STRAIGHT SECTIONS OF HIGHWAY WITH TWO LANES IN PLATEAU

Yuan Zhang , Yulong He ,Xiaoduan Sun ,Bingbing Feng , Yixin Chen

ABSTRACT: There is directly relationship between vehicle speed difference and traffic crashes. In order to improve traffic safety in high altitude area, relationship between altitude and speed was reached in this paper. Speed affects by many factors (road alignment, slope, road condition), to minimize the influence of factors except altitude on speed, this paper selects straight sections of 109 national highway (second-class highway with two lanes) in Qinghai-Tibet plateau. Metrocount was used to collect data. Based on the significant analysis and regression fitting, the influence of altitude to cars’ and trucks’ speed and speed difference was analysis, and models of speed and altitude were built. The results show that second-class highway with two lanes in Qinghai-Tibet plateau, the drop rate of the car speed is smaller than truck speed. When trucks travelled up to 3300 meters high or cars travelled up to 3700 meters high, the speed will gradually decrease and the drop rate will increase with the increase of altitude. With the increase of altitude the speed difference of car and truck gradually increase, when vehicles travel up to 4320 meters high, speed difference will be more than 20km/h.

Keywords: traffic safety, free flow, altitude, operating speed, speed difference.