Research on Relationship between Operating Speed and Posted Speed Limit for Mountainous Freeway

Setting reasonable speed limits is an efficient measure to improve the safety of freeways in mountainous areas. Twenty-five typical sections randomly selected from Xihan Freeway and Qinglian Freeway in China were investigated. On the basis of analyzing the data of 25 sections, speed distributions for cars and trucks under different speed limits were obtained. The correlation between operating speed and posted speed limit of mountainous freeways is analyzed. By means of regression analysis, the relationship model between the 85th percentile speed and posted speed limit, 50th percentile speed and posted speed limit, 15th percentile speed and posted speed limit are established respectively. The regression analysis of posted speed limits and operating speeds shows that there exists a strong linear relationship between these two speed concepts. The 15th percentile speed model is the best fitting model among the three.