Study On Dynamic Traffic Assignment Of Urban Road Network In Snowfall Conditions

The operational status of road network in snowfall conditions is quitedifferent from that in general conditions. In snowfall conditions, thephenomenon of traffic congestion is more than that in general conditions, andthe traffic degree of safety for pedestrian and cars also reduces, which willseriously affect daily trip of people and the normal operation of traffic system.Study on dynamic traffic assignment in snowfall conditions of urban roadnetwork makes an important practical sense and practical value. It can help toestimate the operational status of the road network in snowfall conditions, andalso can provide the suggestions for traffic management in snowfall conditionsof different grades.Firstly, it analyzes the characteristics of snowfall weather and the influenceof road network in snowfall conditions, divide ranks for the snowfall weather,and do survey of traffic flow characteristic parameters in different gradesnowfall conditions. Analyze the survey results and obtain the change tendencyand law of traffic flow characteristic parameters in snowfall conditions.Secondly, based on the traffic survey in different grade snowfall conditions,do regression analysis of the survey data and build the calculation model for thelink free flow speed and the link capacity in snowfall conditions, then model thelink travel time impedance function for snowfall conditions. According to thesaturation of entrance lanes, the study of intersection impedance function isbuilt based on the improved Webster and Akcelik calculation model in snowfallconditions for the signal control intersections. Combining the link impedancefunction and intersection impedance function in snowfall conditions, build thetravel time impedance function model for road network in the snowfallconditions.Thirdly, after the model building of the travel time impedance function insnowfall conditions, it studies on the dynamic traffic assignment model insnowfall conditions. According to the characteristics of snowfall weather,analyze the principle for the dynamic traffic assignment in snowfall conditions.The result is that the principle is stochastic dynamic traffic assignment. Define the model symbol and the constraint condition for the stochastic dynamic trafficassignment model in snowfall conditions, then build the dynamic impedancefunction in snowfall conditions and discretize it. Analyze the randomness ofstochastic dynamic traffic assignment in snowfall conditions. Based on theLogit model, built the stochastic dynamic traffic assignment model in snowfallconditions and design the model algorithm.Lastly, it makes a practical application of road network in ChangChun citycenter. Use the traffic planning software VISSUM11 to conduct stochasticdynamic traffic assignment in snowfall conditions. It obtains the results ofstochastic dynamic traffic assignment of road network in ChangChun city centerin different grade snowfall conditions and normal weather, and also calculatethe characteristic matrix of average travel time and average travel speedbetween traffic zones. compare and analyze the assignment results in differentweather conditions, use related indexes to estimate the operational status of theroad network. At last, give the measures and suggestions for traffic managementin snowfall conditions.