Analysis On The Characteristics Of Vehicle Speed And Acceleration In The Turning Curve Section Of The Mountainous Low-grade Highway

Mountain roads are prone to serious traffic accidents,which threaten people’s lives and property.However,suburb districts in China are composed of 2/3 of the country’s land area.Therefore,it is urgent to improve the safety of the country roads.Although there are many kinds of research on the alignment,speed and trajectory of mountain roads,they mainly focus on highway alignment design or better road conditions.There is a lack of research on low-grade roads.Besides,most of China’s current standards are for high-grade highways,and the practicability of low-grade highways needs to be improved.Thence,the research on the speed and acceleration characteristics of the turning curve of low-grade highways has a significance on improving the safety of country roads and the road alignment design theory.This paper selects a low-grade highway in Pengshui County,Chongqing City,with a design level of 4 and 12 turning curves.This experiment employed 20 experienced drivers to drive an experimental vehicle equipped with a high-precision inertial measurement system to obtain a large amount of speed and acceleration data of the turning back curve part under normal condition.Using MATLAB,EXCEL and other data processing software to perform mathematical-statistical analysis on the experimental data.The results are as follows:（1）Through researching the turning curve speed,it is clear that the turning curve uphill speed mode is"deceleration-acceleration",which is obviously different from the downhill speed mode"deceleration-constant speed-acceleration".（2）The data regarding the location where the drivers reach the lowest velocity has been assessed.The lowest point of the uphill has a higher degree of discretion than that in the downhill,mainly distributed between the HY-GQ points;the lowest point of the downhill deceleration is between the ZH-QZ points,and the acceleration starting point occurs after the GQ point while it started to accelerate within the GQ-YH point interval.（3）Finding the characteristics of longitudinal acceleration of the turning back curve in the peak and lowest location.The value of the uphill curve is generally lower than1.5m/s².The peak value of acceleration is located at the HZ point after leaving the curve,which is generally greater than 1.5m/s².The lowest position is mainly distributed between the ZH～HY points.The peak value of acceleration downhill is mainly distributed on the slope,and the peak value of acceleration is mainly located near the HZ point after exiting the bend.The lowest value of deceleration is mainly distributed before the ZH point.（4）The correlation analysis between the driver’s speed change amplitude characteristics and acceleration and deceleration in the turning curve section is obtained.The sudden change points of the uphill acceleration and deceleration variable-length curvature are all around the 85^th quintile,and the acceleration and deceleration lengths are 266.867m and 158.582m,respectively.The sudden change point of downhill shifting curvature is near the 95^th quintile.Its acceleration and deceleration lengths are 194.479m and 185.989m,respectively,which can provide a theoretical basis for the setting of speed limit signs.（5）The five types of lateral acceleration modes of the turning curve are obtained,and by comparing the mean value of the turning curve with the general turning acceleration,it is found that in the 85^th percentile,the difference between the two is 0.5m/s²,so in the horizontal line of the turning curve Acceleration cannot be used mechanically with the existing research on the horizontal acceleration,which also reflects the significance and necessity of this article for the research on the horizontal acceleration of the turning back curve.（6）Based on the results of the research on the speed and acceleration of the turning curve,the operating speed models of the turning curve in the deceleration phase,in the curve,and acceleration phase when exiting the turn,were established respectively.The research of the thesis provides a scientific basis for the operation management,safety improvement,calculation model revision and design specification revision of the turning curve of low-grade highways,and promotes the development of the theory and technology of the safety evaluation of turning curve.