Research On Road Traffic Assignment Algorithms Based On WebGIS

Reasonable traffic demand forecasting is the premise and guarantee of excellent traffic planning scheme,and an important technical support to treat urban traffic problems.However,in addition to the TranStar developed by Professor Wang Wei’s team from Southeast University,the traffic demand forecasting methods are almost achieved through software developed abroad,such as TransCAD,Cube,Emme and VISUM,which lacks the demand forecasting tool of independent intellectual property.Not only that,these programs are also cumbersome and complex,and the principle of implementing internal algorithms is not open.Therefore,it is necessary to explore and develop traffic demand forecasting programs with good graphic display effect,friendly interaction interface and open source characteristics with new technology.Thus,promotes the domestic traffic programs technology research and development ability.Traffic assignment is the most important part in demand forecasting.First,this paper reviews the current situation of demand forecasting programs research,searching the common traffic assignment methods at home and abroad,and the application of WebGIS technology in traffic analysis.By searching and discovering,the WebGIS has been widely used in various industries with its wide audience,platform independence,high efficiency computing power and unified update.Secondly,the paper studies the relevant technology of WebGIS,compared with the current mainstream application technology.And select the open source frame for the development system.Then the paper realized the modeling of the road traffic network and the method of connecting with the OD data in the process of analyzing the road traffic assignment.And four shortest path methods with centroid connectors are presented fixed resistance method,dynamic resistance method,exclusive method and principle method.And by combining the technique and theory of accumulation,the algorithm of road traffic assignment based on the WebGIS is developed.Implementation of data upload,the shortest path method selection,assignment method selection and visual analysis functions.In addition,the paper also constructs a user equilibrium algorithm process based on JavaScript.Finally,by comparing the accuracy and speed of calculation by Floyd and Dijkstra,and by comparing the assignment results with common programming software,TransCAD and Cube,the accuracy and practicability of WebGIS assignment algorithm is verified by using the method of spatial distribution and non-parameter test of traffic volume.In the case given in the paper,the research results of traffic assignment algorithm based on WebGIS technology show:(1)The assignment results of Floyd and Dijkstra algorithm using dynamic impedance method are the same,and the running speed is below 500 ms.However,the Dijkstra algorithm was 11%,35% and 10% higher than the Floyd algorithm in all-or-nothing,method of successive average and user equilibrium algorithm.(2)By comparing the distribution results with TransCAD and Cube,in running time,the WebGIS-based traffic assignment program which choose Dijkstra shortest path is 221.02 ms,262.91 ms,and 297.55 ms in all-ornothing,method of successive average and user equilibrium algorithm.it is 3.17 times and 2.28 times of TransCAD for all-or-nothing algorithm and user equilibrium algorithm respectively.In the visual analysis,user-defined and aesthetic visual analysis can be achieved.In the assignment result,the average relative error between the three assignment results and the result of TransCAD was 0%,16% and 1% respectively.The average relative error with Cube is 0%,46% and 0% respectively.