| Transporrtation network accessibility is an important model of regional traffic network.This paper takes the inner area of Xi’an city circumferential expressway as the research object.,constructs traffic network geodatabase firstly,based on graph theory and combined with geographic information system spatial analysis technology,chooses the four indicators of road density,road network area density,the road network connectivity and connection rate of public transport network to analyze the accessibility of Xi’an traffic network.And select the OD matrix to measure the distance of accessibility,the selection method of the area when the ring type accessibility measure,analysis of Xi’an city traffic network accessibility situation.Aiming at the two states of Xi’an Metro’s running route and planned route,this paper measures the traffic accessibility and its pattern changes before and after the completion of the Metro through multiple indicators,analyses the results of Xi’an Metro network accessibility,explores the impact of subway construction on Xi’an’s traffic network accessibility,and analyses the relative accessibility changes before and after the opening of the mainland railway in different regions.The main conclusions are as follows:(1)The road density in the study area is 1.02km/km2,indicating that the regional transportation network is dense and the road network system is perfect.The road area density is 7.31%,and the road occupation ratio is low,indicating that the road planning in Xi’an needs further improvement.The road network connection degree is 3.13,which indicates that the road network in the study area presents a complex mixed layout of ring and square grids,and there are f’ewer broken roads.The connection rate of public transport network is 3.15,indicating that the public transportation network in the study area presents a good loop structure.(2)The comprehensive time accessibi:lity index is 0.04 with the connection point of the main road as the starting point and the bell tower as the terminal point.The accessibility of each node is quite different.In different pernods and modes of transportation,the scope of traffic services varies greatly.In the spatial form of node formation,Xi’an road network obviously presents the characteristics of accessibility Extension determined by the main road,along the main road to form a higher accessibility index corridor,and in the region shows the characteristics of high accessibility of the old urban area,gradually decreasing outward extension.(3)Establishing the road network database after joining the metro,it is concluded that the overall time accessibility of the study area is 0.09,up by 56%.Moreover,the comprehensive time accessibility index of each node has increased significantly,and the difference of each node has increased.This shows that the accessibility of Xi’an road traffic network has increased significantly after the opening of the subway,and the convenience of residents has increased significantly.The relative accessibility of the study area reflects that the opening of the Metro has reduced the total time cost and average time cost of all the districts in the study area.The improvement rate of total time cost and relative average time cost is the highest in Northeast China(Ⅱ),which saves 52.04%and 51.94%of the time cost before opening.(4)According to the latest construction plan,the fifth,sixth,seventh and eighth lines in the study area are selected as the planning lines,and the road network database after planning is established.It is concluded that the comprehensive time accessibility of the study area is 0.10 after joining the planned metro,60%higher than that without joining the metro,11%higher than that under the existing metro network,and the total time cost of the regional relative accessibility is improved.In order to be obvious,the Northwest(Ⅱ)has the largest improvement rate in a single area,saving 19.13%of the time cost of the existing subway network,and the southwest(Ⅱ)has the largest improvement rate in the relative average time cost,saving 25.21%.(5)The opening of Metro makes the total time cost and average time cost of all zones in the study area reduced.After the completion of the metro,the absolute accessibility of the periphery of the region increases more than that of the central region,and the "radius trap"makes the relative accessibility of the central region higher than that of the periphery,resulting in the change of the accessibility character of"central expansion-periphery collapse".The research results can provide a basis for evaluating Xi’an road traffic network and planning roads,embody the optimization role of subway construction,and provide a reference for the later planning of Xi an traffic network. |
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