Designing Criteria of Continuous Long Slope Alignment at Alpine and High Altitude Area Based on Reliability Analysis

The main objective of this paper is to bring forward the flexible method for designing the continuous downgrade alignment at alpine high altitude area. Brake fade of trucks is the most important cause of accidents on this special alignment, and therefore, temperature rise model is the theoretical core for alignment criteria selection. Several researches have been carried out for laws of temperature rising of trucks on downgrade at low altitude area under normal climate. Additionally, deterministic method is always the basis of guidelines for road designers. However, when situation changes to alpine and high altitude condition, temperature does not rise as imagined, and deterministic method has limitations in specific circumstances. This paper collects data on two roads in Tibet, one for lower gradient, the other for higher gradient. As drivers have different driving behaviors on the two roads, this paper divides temperature rise model into two parts based on the gradient. After two Chinese temperature rise models are corrected by data from Tibet with R-squares beyond 0.8, reliability analysis is then carried out. Speed and weight are hypothesized as normal distribution, and then reliability is calculated. Consequently, the relation between restricted slope and grade is given under certain limited state. The flowchart of design criteria is shown against different districts finally.