Reliability Design Method for Long Steep Downgrades Based on Trucks' Braking Safety

Long steep downgrades are typical accident-prone highway sections. To solve this problem, a reliability design method for long steep downgrades based on the braking safety of truck was presented. Based on Unified Standard for Reliability Design of Highway Engineering Structures, the term of reliability of downgrade was defined. With the critical safety temperature of braking efficiency drop as a constraint, the performance function of brake's temperature rising model was established. A model for calculating downgrade's reliability was deduced and method for solving the model was put forward. Combined with an example, the reliability of the accident-prone highway sections was obtained. The results show that the application of the downgrade reliability design method is illustrated, and its reasonability is verified. Furthermore, with the reliability design method, the maximum safety grade length of combined downgrades of expressway was calculated.