Optimizing Speed Limits Upstream of Freeway Reconstruction and Expansion Work Zones Based on Driver Characteristics

Traffic incidents occurring in freeway work zones mainly include rear-end accidents and roadside accidents, as well as collisions between vehicles and traffic facilities and construction personnel. Speeding is the key factor causing all these incidents. Therefore, in this study, to ensure the construction and traffic safety in the process of freeway reconstruction and expansion, the setting of speed limit signs in a traffic-free flow state upstream of the work zones is investigated. Based on the analysis of the braking and visual characteristics of drivers, two new approaches are proposed for individually calculating the speed limit values and spacing among the gradient speed limit signs (GSLS) upstream of the work zones. Subsequently, these approaches are applied to the reconstruction and expansion engineering project from Jilin to Longjia Airport on the Huiwu Freeway. The research results show that when the design speed is 120  km/h120  km/h, the maximum daytime speed limit upstream of the freeway reconstruction and expansion work zones is 100  km/h100  km/h, and it is appropriate to set the speed limit in decrements of 20  km/h20  km/h; also, the maximum nighttime speed limit is 110  km/h110  km/h, and it is appropriate to set the speed limit in decrements of 10  km/h10  km/h. A positive linear relationship exists between the spacing and speed limit values, and the spacing among the nighttime speed limit signs is greater than that for the daytime speed limit signs.