| Road traffic system which is one of the lifeline systems is the important foundation of urban economic and social development. Its running state and stability is directly related to people's lives, property security and national economic development. How to improve the urban road network operation stability and ensure the lifeline road traffic system function performing properly have abstracted a lot of interest from the society particularly in the traffic-engineering field in recent years. Research practice shows that reserching on the urban road network reliability has a promoting effect on the improvement of network planning, disaster relief, traffic management and so on.The road network travel time reliability under ice and snowfall conditions was systematically studied. Aimed at putting forward the road network travel time reliability evaluation methodology with the consideration of the characteristics of transportation system under ice and snowfall conditions, providing the reliability evaluation indexes and references of network reliability assessment under these conditions, and providing theoretical support for the urban traffic planning, management, emergency relief etc.On the basis of analysing the characteristics of the urban transportation under ice and snowfall conditions, the travel time reliability of the urban road network elements——links and intersections and the generalized travel cost can be studied, By regarding the reliability theory as the basis of the research ideas using the transportation research, probability and mathematical statistics, numerical analysis, Monte Carlo simulation , mathematical planning model and other methods and combining the basic theory and the application . Then the urban road network reliability under ice and snowfall conditions can be studied basing on the generalized travel cost.Through extensive investigation and analysis of traffic survey data, link and intersection traffic flow characteristics under different ice and snowfall conditions were studied, including vehicle's arrival-distribution at link, headway distribution, speed and traffic flow volume changing rules, intersections'saturated flow rate, running speed and critical accepted headway and following headway distribution, etc, and comparative analysis was made to traffic characteristics corresponding to the normal weather conditions, providing the basis for the follow-up study.Based on the analysis of the relevant theories and field observation data, modified functions of the link free travel time and capacity under ice and snowfall conditions were introduced, ISB-BPR (Ice and Snowfall Based-Bureau of Public Roads) travel time function was established and parameters calibration were done respectively according to the field observation data in Harbin and Weihai. According to the limitations analysis for the conception of present travel time reliability, it was defined in this paper. Combining with the calibrated ISB-BPR function, link travel time reliability model under ice and snowfall conditions was established. In order to facilitate the comparison of reliability evaluation results and the information application, benchmark of LOS for reliability evaluation was set, travel time expectation under different LOS was determined, and the reliability evaluation results were divided according to hierarchies. Additionally, according to the model features, Monte Carlo simulation algorithm was put forward, travel time reliability evaluation methodology under ice and snowfall conditions was established, which effectiveness was verified through example, and influencing factors of the travel time reliability were analyzed.In order to improve the previous travel time research assumptions, using a more reasonable M3 distribution and combination negative distribution to describe the straight-going vehicles and non-motor vehicle headway at intersections respectively, left-turning and right-turning vehicles travel time models through intersections were founded by using gap theory and queuing theory, providing the models that can be suitable for the urban traffic at intersections. In addition, considering traffic conflict between straight-going and left-turning flows, straight-going vehicles travel time model through intersections was modified, combined with the constructed travel time models of different direction, intersection travel time reliability evaluation models were established by considering different flow driveway group as the basic unit. LOS for intersection travel time reliability evaluation was set, and the reliability evaluation result was divided into hierarchies, finally travel time reliability evaluation methodology at intersections under ice and snowfall conditions was proposed. Afterwards, its effectiveness was verified by example, and the intersection travel time reliability under ice and snowfall conditions influencing factors were analyzed.Based on the analysis of the travelers behavior characteristics under ice and snowfall conditions and safety, generalized travel cost functions of link and intersection were defined respectively. The safety factor of driving on the ramp was introduced, using the inverse of the safety factor to quantify the safety cost index of driving under ice and snowfall conditions, and travel attitude towards risk was reflected using different weight coefficients. To eliminate the original dimensional influence, each index was conducted to one without dimension. Based on the change of traffic demand under ice and snowfall conditions, EDUE, which is based on generalized travel cost, was established. Breakthrough of the traditional idea that route travel time reliability model was set by general series system by considering route as a whole unit was made, another breakthrough is that not using a paralleling system on the reliability of the travel time OD (Origin Destination), but for each route of OD the weighted average travel time reliability, on the base of OD travel time reliability, the road network reliability model was set up. Finally, the effectiveness and practicality of the evaluation methodology was validated by being applied to the partial road network travel time reliability evaluation in Harbin and Weihai. And comparisons of evaluation results were done between the above cities.
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