Necessity Analysis of inside Shoulder for Multi-lane Freeway

By the end of 2014, the total mileages of freeway in China have reached 112,000 kilometers, ranking the first in the world. Most of freeways are four-lane or six-lane, for which inside shoulder is not required by current Chinese guidelines. The inside shoulder is designed to reduce the possibility of fatal traffic accidents on freeways. In China, “Technical Standard of Highway Engineering” regulates that 2.5-meter width inside shoulder should be provided in eight-lane freeways. Several old four-lane or six-lane freeways have just been reconstructed into eight-lane roadways without adding inside shoulder, and even without side strips wider than 0.75 meter. Meanwhile, few studies have systematically analyzed the advantages of inside shoulder for multi-lane freeway. Based on the statistical analysis of accident data, the theoretical modeling and simulation of lane-changing theory, as well as the cost-benefit analysis, this paper studied the effects of inside shoulder on the operational efficiency and traffic safety, and further demonstrated the necessity and feasibility of inside shoulder for the multi-lane freeways.