Study On The Setting Of Compulsory Parking Area For Long Down-slope Of Expressway

Traffic accidents caused by brake failure of large trucks occur frequently in the continuous long down-slope of mountain expressway.Compulsory parking areas adopt an active accident avoidance strategy to reduce the accident probability directly thus has obtained the expressway operator and the management side more and more attention.The reasonable setting of compulsory parking area can not only improve the road passage safety,but also avoid the waste of land resources,so as to give full play to the function of compulsory parking area.In this paper,the brake system,brake principle and brake heat fading mechanism of large truck under the condition of long down-slope are analyzed comprehensively.The application of temperature rise model of brake hub is discussed at the same time.Force analysis on the large truck when braking is carried out,torque analysis on the rear wheel when braking is carried out,and the relationship between braking deceleration speed and rear wheel braking torque is obtained by integrating relevant parameters.The braking model of large truck under the condition of long down-slope was established.On the basis of the large truck braking model,this paper studies the setting of compulsory parking area with the reliability method:Based on the analysis of the braking reliability of the big truck from the Angle of the main traffic accident on the long down-slope section,the limit states of the big truck avoiding collision and the big truck avoiding rear-end collision under the condition of single vehicle are obtained.The parameters in the limit state are analyzed and calibrated.The actual running speed of vehicles in the long down-slope section from lanzhou south toll station to xinqidaolang tunnel of lanzhou lanhai expressway was investigated on site and the investigation results were analyzed.The results show that the vehicle velocity distribution at the top,middle and bottom of the slope obeys normal distribution.EQ1208 produced by dongfeng company is selected as the leading model,and the expected distribution of braking deceleration speed is obtained by using the temperature rise model of braking hub and the braking model of large truck,and determine the compulsory parking area setting requirements calculated by the reliability under the condition of following the car.The calculation results show that: in order to guarantee the 90% reliable probability of the large truck brake deceleration,the brake recession rate should be below 34% and the brake hub temperature should be below 290℃.Based on the calculation of the temperature rise model of the braking hub,the spacing requirements for the compulsory parking area under different slopes are obtained.When the average longitudinal slope is 2.5%,the maximum spacing is 30 km.When the average longitudinal slope is 3%,the maximum spacing is 16.3km.When the average longitudinal slope is 3.5%,the maximum spacing is 10.7km.The method of compulsory parking area is applied to the expressway project from jianshui(gejiu)to yuanyang in honghe prefecture,and put forward the suggested location of compulsory parking area.In addition,from the perspective of human-oriented and safety-first,this paper puts forward some Suggestions on the combination of compulsory parking areas and safe-haven lanes.