Research On Expressway Traffic Flow Characteristics, Traffic Guidance And Control Under Adverse Weather

Adverse weather such as rain, snow, fog and so on brings a bad influence on road traffic safety and highway network operation. Statistically, about one- third of the block incidents on arterial network have been caused by adverse weather. Adverse environmental conditions for driving such as fog, snow and ice clad roads lead to the increasing rate of road accidents. At present,the research and application of traffic management under adverse weather condition is still at a starting phase in China. Most research learns from foreign early technology and experience to strengthen road weather monitoring and information dissemination by facilities such as variable massage sign. In recent years,highway and meteorology bureaus have strengthen cooperation, and have made progress in detailed road weather forecast and service. Compared with the developed countries, research on safety enhancement technology and facilities developed its own features. However, research on basic theory of traffic flow characteristics, traffic guidance and control under adverse weather condition, the convergence between traffic weather information and traffic management, assistance decision support and so on, still fall behind compared with the developed countries. Under the background of global warming and rising emergency incidents caused by extreme weather, it is necessary and urgent to study on traffic guidance and control in adverse weather and it will help decrease detrimental effects on highway system.The research purpose of this paper is to improve expressway management ability under adverse weather condition. Several key points including traffic flow characteristics, short-time prediction of link travel time, road network flow assignment and expressway management and control under adverse weather condition will be studied.Traffic flow characteristics under adverse weather condition provide the groundwork for analysis of expressway capacity and management and control measures. However, it is very difficult to get enough high quality data of traffic flow and related weather information, which seriously restricts the study on traffic flow characteristics. Using traffic flow and related weather data of Jinggangao Expressway in Hubei province, this paper studies the influence of rainfall intensity in rainy weather and visibility level in foggy weather upon vehicle mean speed and speed dispersion compared with good weather. It also studies speed difference in different traffic lane, different vehicle type and different time. Based on Greenshield’s traffic flow V-K model, this paper establishes a multifactorial comprehensive predicting model of average speed using non-linear regression.The average link travel time of expressway is a key factor to provide information service to travelers and construct road impedance function, which can make traffic assignment and then implement traffic guidance. At present, prediction technology of link travel time appears trends from single method to multiple methods. To meet the demand of accuracy and simplicity and availability, this paper selects weather data such as rain and fog and traffic flow data collecting from Jinggangao Expressway in Hubei province, and constructs prediction model of exponential smoothing method, prediction model of improved neural network based on quasi- Newton methods. This paper also constructs an assembled forecast model of exponential smoothing method and improved neural network based on quasi- Newton methods by using multiple regression method. After comparison of accuracy and error distribution, the assembled forecast model greatly increases the accuracy and reliability of common prediction method.At present,research on road impedance function is limited to directly using travel time or travel cost as road impedance value, however the influence of distance,travel cost and level of service on route choice behaviors are not considered comprehensively. Therefore, this paper proposes a construction method for road impedance function based on subjective wishes or preference. This paper collects the initial data through the questionnaire and gets parameters by statistic regression analysis. This paper provides that road impedance is a function of average link travel time or average speed and distance,and demonstrates applicability of road impedance function based on traffic assignment example.This paper proposes a method to determine appropriate speed limit against the existing problems. This method can consider some traffic and weather factors such as pavement friction, sight distance, traffic combination and flow. Division and threshold of pavement slippery index is proposed, and speed control criteria under different traffic flow rate and visibility conditions is provided. This paper presents three interdepartmental and interregional joint coordination mechanisms including coordination of traffic management and control, dispatching of CCTV resources, and information sharing and coordinated dissemination. Taking typical adverse weather such as poor visibility caused by fog and wet icy road for example,this paper proposes coordinated schemes for highway network control under different grade of incidents. Additionally, this paper puts forward the procedure of coordinated information dissemination based on variable massage sign, and strategies for variable information dissemination based on their information decomposition and position classification. The study results are tested and validated in Huning expressway traffic management center.Based on a large amount of data, traffic flow characteristics on expressway under adverse weather condition are deeply researched. A multifactorial comprehensive predicting model of average speed is established. This paper constructs prediction model of average link travel time based on quasi- Newton methods, further proposes a combination prediction model based on exponential smoothing method and neural network method. This paper also puts forward a construction method for road impedance function based on subjective wishes and corresponding parametric determination method. Additionally, this paper studies determining method of appropriate speed limit for expressway, traffic management, control strategies and coordinated information dissemination. Several achievements in traffic flow characteristics and traffic management and control technologies for expressway under adverse weather condition have been made, which will provide theory and technology support for improving operation and incident management for expressways or highway network to deal with influence of adverse weather on road traffic system.