The long-steep downgrade sections of expressways are characterized by a large elevation difference, poor horizontal and vertical alignment, and the easy failure of brakes on large trucks. They are sections with a high overall operation safety risk. It is necessary to strengthen the research on traffic risk evaluation. In order to study the traffic safety risks of long-steep downgrade parts of expressways, the fuzzy hierarchical comprehensive evaluation method is used to establish the calculation model. First, an evaluation index system including the target level, rule level, first-level index level and second-level index level is established. The qualitative and quantitative indicators are processed by the set value statistical method and the linear standard method, respectively, so that all indicators can be quantitatively evaluated together. Then, each indicator is assigned a score and divided into five risk levels, and a ridge-shaped fuzzy distribution is used to constitute a membership function for each level. A hierarchical structure model is established with the analytic hierarchy process to determine the affiliation between the upper and lower levels, and the relative weight of each level to the upper level also can be obtained. Finally, according to the hierarchical relevance of each evaluation indicator, a three-level fuzzy comprehensive evaluation model is constructed. The traffic risk evaluation level for long-steep downgrade sections can be obtained, and the probability of the corresponding risk evaluation level can be calculated. Through the risk evaluation of the long-steep downgrade sections of the Fuzhou Yinchuan Expressway in China, this shows that the risk evaluation conclusion obtained by using this evaluation method is consistent with the actual traffic safety situation, which shows that the traffic safety risk evaluation model based on a fuzzy hierarchy comprehensive evaluation is operable.

The formulation of the current geometric design standard for freeways considers the influence of the “human-vehicles-road-environment” system. In the fully autonomous environment, the driver has been liberated from the system, which means that the influence of “human” will be reduced. The requirements or limitations of the freeway geometric design standard, which consider the driver’s psychological and physical factors in the traditional driving environment, can be more flexible in the fully automatic driving environment. By using the methods of comparative analysis, theoretical analysis, and theoretical calculation, this article researches the geometric design standard for freeways in an autonomous driving environment from four aspects: control elements of geometric design, horizontal alignment, vertical alignment, and cross-section elements. The main contribution of this article is to propose the recommended values of the geometric design standard for freeways in a fully autonomous driving environment, which can provide reference for the formulation of relevant standards or specifications for autonomous driving roads in the future.