Study On The Key Problems Of Planning And Design Of Experssway In A Big City

To ease the growing pressure on urban traffic, protect the centres of big cities, and to keep an effective separation between the long-distance traffic and the short-distance traffic, allow the city roads and transit highways to be a reasonable transition and convergence, many cities began the planning and construction of expressways.In this process, we will face many key problems such as how to determine the scale of expressway, how to plan the road network, the choice of road patterns, how to plan and design the nodes, etc.Firstly, the paper expound on the origin and causes of the expressway, review the course of development of urban expressway in the west cities and our cities, analyze the functions of expressway system in the urban road network, research traffic characteristics and the construction conditions of expressway. And then the paper classify the patterns of expressway, note the patterns'respective advantages and disadvantages; research the lane numbers and width from the perspective of traffic safety and traffic capacity; To enhance the efficiency of expressway, the paper bring up five BRT layout patterns for the viaduct and ground expressway.This paper summarize and bring up three methods that confirm the reasonable scale of urban expressway: the density law, the law of supply and demand balance and analogy law; and then bring up the layout method of urban expressway network, which based on traffic unit deviding, and the specific layout planning process of urban expressway network.The paper summarizes the commom types of expressway interchange, analyzes their advantages & disadvantages, then bring up improvements. It researchs the smallest distance between ramps, and bring up a methodology based on gap acceptance theory, which decide the design length of the ground interweave road. From the perspective of traffic design, makes the optimized designs to connect the traffic between ramp and auxiliary road.It also establishs an index system for evaluating the planning programmes of expressway network, and analyzes detailedly these indices and provides the methodologies; and then establishs a evalution method which based on entropy method and comprehensive fuzzy.Finally, the paper gives Tianjin as an example.