城市道路是城市发展中人流和物资实现转移的重要通道，是城市发展的主要动力，对生产要素的流动有着决定性的影响。但是随着全球气候的变暖，极端天气出现的频率增加，使本就捉襟见肘的城市交通系统面临着更大的考验，交通安全和交通拥堵问题越来越突出，严重影响城市居民的工作和生活，带来了极大的环境污染和经济损失问题。若能分析得到城市道路交通流运行特性受天气影响的规律，则能为不利天气条件下交通管理和控制提供科学的依据。然而，当前对于交通流特性的研究均基于正常天气条件下，当遭受到降雨和能见度下降等不利天气时，城市道路交通流运行特性发生较为显著的改变，城市快速路和地面道路的偶发性拥堵便从点到线、由线及面蔓延开来，造成了大范围较严重的交通拥堵。因此研究交通运行特性在各种天气条件下的变化规律具有十分重要的现实和理论意义。

       本文在总结国内外研究的基础上，选取上海市的城市快速路和信号控制交叉口为研究对象，综合运用交通流理论、交通工程、概率论与数理统计、模型拟合的手段，分别对不同交通状态条件下交通流运行特性受天气的影响规律进行了研究分析，研究工作如下：

       首先，通过交通气象、交通流运行特性和天气对交通流运行特性的影响三方面对国内外的研究现状进行了梳理，并基于《汽车道路试验方法通则》和目前的气象学天气等级分级标准，从车辆运行的角度出发，对常发的降雨和大雾天气对交通流运行特性的影响因素进行了理论分析，并指出降雨和大雾主要通过能见度和路面摩擦系数的改变对运行车辆产生不利的影响。

       接着，选取上海市快速路路段为研究对象，利用环形线圈采集的交通数据和徐家汇气象站所观测到的天气数据，以晴朗天气条件下交通流的运行特性作参照，深入地对比分析了上海市城市快速路交通流运行特性受降雨和大雾天气影响的程度及其变化规律，绘制了不同天气条件下的流-密-速基本图，并进行了数理统计、模型回归分析，分别从定性和定量两个层面研究了上海市城市快速路路段的交通流运行速度、通行能力和横向分布特性在受到天气影响时的变化规律。结果表明降雨和大雾能较为显著地降低交通流运行速度和通行能力，而二、三和四车道断面的横向分布特性主要受断面流量的影响。

       最后，选取了不同种类的城市地面道路中信号控制交叉口的直行车道和左转专用车道为研究对象，采用视频拍摄的方法获取了晴朗和降雨天气条件下的车头时距。并以晴朗天气条件下的交通流运行的规律为参照，对比分析了降雨天气条件下不同功能的车道和不同车型组合的情况下饱和车头时距和饱和流量的变化。结果表明降雨能够使车辆饱和车头时距增加，而降低进口道的饱和流率；左转车道的饱和车头时距大于直行车道的饱和车头时距，饱和流率小于直行车道的饱和流率；当前车为大车时，车辆的车头时距会有明显的降低。

       本文在现有研究的基础上，分别从城市快速路路段和信号控制交叉口入手，全面深入的分析了天气对城市道路交通流运行特性的影响规律，为城市交通系统的管理和控制提供了科学依据，丰富了交通流领域的研究，具有十分重要的理论和现实意义。

    Urban transportation system is an important channel for travelling of people and transiting of goods in urban development. As a main driving force, urban transportation system is decisive of the transition of factors of production. Global warming leads to an increase in the frequency of adverse weather, which leads to traffic safety and congestions problems. It no doubt affects daily life of urban residents and brings more stress on road network system, environmental protection and economic development. So analysis of traffic-flow characteristics under adverse weather is the scientific basis for traffic control and management under that weather. Most of the researches on traffic-flow characteristics focus on performance on good weather. However, performances urban road network is worse due to rainfall or low visibility than that on good weather. Congestion begins from a point to a main line and spreads over an area on adverse weather, which may not happen on good weather. So it is very important to analysis the traffic-flow characteristics considering weather conditions both in theory and practice.

    Based on a summary of the research at home and abroad, this dissertation uses urban freeways and signalized intersections in Shanghai as main research objects. Traffic flow theory, traffic engineering, probability and mathematical statistics, and model fitting statistics are integrated to analyze how the traffic-flow characteristics are affected by the weather under different traffic conditions. The logic of this dissertation is as follows:

    First, a systematic summary of the research on traffic meteorology, traffic-flow characteristics and how the weather affects the traffic-flow characteristics was given. Based on the national standard on weather and the characteristics of vehicle operation, theoretical analysis was used to check how the recurrent rainfall and fog affects the traffic flow and main factors.

    Next, urban freeways in Shanghai were selected as the research objects. Traffic data from loop detections and weather data from weather station in Xujiahui were used to give the quantitative and qualitative analysis on how the recurrent rainfall and fog affects the traffic on urban freeways comparing with the characteristics on good weather. Flow-density-speed curve was drawn as a qualitative analysis and a combination of probability and mathematical statistics and model fitting statistics was used as a quantitative analysis. That analysis leads to a better understanding of how the weather affects the capacity and speed of urban freeways in Shanghai.

    Finally, through lanes and left lanes of urban street with signalized intersections are analyzed. Video was made and analyzed to get the headway on both good and adverse weather. Saturation headway, saturation flow rate and start-up lost time were analyzed comparing the data on good weather with that on adverse weather considering the function of lanes and distribution of vehicle types.

    Based on the existing research, this dissertation focus on the analysis of how the weather affects the traffic-flow characteristics on both urban freeway and signalized intersection. It provides a scientific basis for traffic control and management, enriches the traffic flow theory. It’s very important in both theory and practice.