城市快速路互通立交交织区长度可靠性设计

Reliability Design of Weaving Segment Length of Urban Expressway Interchange

城市快速路中互通立交交织区长度的合理设置将对整个城市快速路系统的服务水平、通行能力、行车安全的提高起到关键作用,有必要对互通立交交织区长度的取值进行科学合理的计算。基于《公路通行能力手册》交织区中的相关方法建立交织区长度的计算模型;以该模型为依托结合可靠度理论,建立最小交织区长度可靠度功能函数,对交织车辆区间平均速度、交织区基本路段的平均自由流车速等随机变量的随机性及其分布规律进行分析。利用蒙特卡罗法讨论现行规范中最小交织区长度设计取值的安全可靠性,用失效概率及可靠指标进行评价。参考《公路工程结构可靠度设计统一标准》中城市快速路对应安全等级的可靠度要求,计算不同设计速度下的交织区长度,并结合实例验证,其计算结果具有较高安全性。研究表明:以150 m作为互通立交交织区长度应用于快速路设计,其失效概率较大且安全性较低;通过以满足一级安全等级条件的目标可靠度反算,推荐在100、80、60 km/h共3种设计速度下,互通立交交织区长度分别取400、370、350 m,可提高整个城市快速路系统的高效性和安全可靠性。

The reasonable setting of the weaving segment length of the interchange section in urban expressway will play a key role in improving the service level,traffic capacity and traffic safety of the whole urban expressway system.Therefore,it is necessary to calculate the weaving segment length of the interchange scientifically and reasonably.Based on the relevant methods of weaving section in Highway Capacity Manual,the calculation model of weaving section length was established.The reliability function of the minimum interweaving area length was established based on the proposed model and the reliability theory.And the randomness and distribution law of random variables such as“average speed of weaving vehicles interval”and“average free flow speed of basic section of weaving section”were analyzed.Monte Carlo method was used to discuss the safety and reliability of the design value of the minimum weaving section length in the current code,and the failure probability and reliability indicators were used for evaluation.With reference to the reliability requirements of the corresponding safety levels of urban expressways in the Uniform Standards for Structural Reliability Design of Highway Engineering,the lengths of weaving section at different design speeds were calculated,and the calculation results were verified to be of high safety by the case study.The results show that:using 150 m as the weaving section length of an interchange in expressway design has a high probability of failure and low safety.By backcalculating the target reliability that meets the conditions of the first level safety level,it is recommended that 400 m,370 m and 350 m are selected respectively for the length of interchange weaving section at three design speeds of 100 km/h,80 km/h and 60 km/h,which can improve the efficiency of the safety and reliability of the whole urban expressway system.