Discussion on Speed Shifting Lane Length of Overpass

In considering shifting lane construction costs,the economic benefits of increasing the length of shifting lane to improve safety was assessed. By constructing benefit- cost ratio( B /C) analysis model,the recommended value of shifting lane length was proposed based on comprehensive consideration of traffic safety and construction costs. The research showed that with the increase of shifting lane length,the initial B /C values shows a growth trend and after the peaking value with the increase of shifting lane length,B /C values slowly decline,the corresponding shifting lane length is selected as the recommended design value.