长江三角洲高速公路网络构建对区域可达性的影响

高速公路建设有利于缩短地区间的交通里程并节约旅行时间，改善区域间的可达性并有利于地区间的经济联系的增强。以长江三角洲地区为研究区域，基于1992、1998、2004和2010年的公路交通网络数据，采用节点平均交通里程、节点平均迂回系数、节点平均旅行时间和区域平均旅行时间等空间和时间距离指标对长三角地区选定年份的交通可达性及其变化进行测算与比较。研究表明：1）各县市平均交通里程均获得了不同程度的缩短，节点平均迂回系数均获得了不同程度的降低，但不同县市在不同时期的改善幅度存在较大差距，2004―2010年各县市平均交通里程改善幅度最大，尤其是跨江和越海通道建设使长江和杭州湾沿岸县市的迂回度获得了较大幅度的降低；2）随着高速公路的建设，各节点平均旅行时间和区域平均旅行时间均获得了大幅度的改善，尤其是边远地区改善幅度更大，但受交通建设边际效应递减规律的限制，可达性的改善幅度不断减弱。

Impact of Expressway Network Construction on the Regional Accessibility in the Yangtze River Delta

The basic spatial economic efficiency of expressway network construction is to shorten regional travel mileage and travel time, which will be propitious to improve the regional traffic accessibility level and strengthen regional socio-economic linkage. Since the 1990s, the expressway in the Yangtze River Delta has experienced initial development stage, linear expansion stage, network construction stage and network promotion stage. With the large-scale construction of expressway infrastructure, the regional expressway network scale has been expanded significantly, the network connection degree has been improved and the network structure has been optimized continuously, whose direct spatial economic effect is to promote spatial-temporal accessibility in the Yangtze River Delta. In the paper, the Yangtze River Delta is taken as a research scope, the spatial-temporal accessibility level and changes are calculated and compared by the model of node average traffic mileage, node average circuitous coefficient, node average travel time and regional average travel time, based on the database of highway network in the Yangtze River Delta in 1992, 1998, 2004 and 2010. The results show that: 1) Average traffic mileage of each county has been shortened, and the average circuitous coefficient has also reduced greatly, but the variation range disparity is remarkable in different development stages and among different counties, especially, the variation range of node average traffic mileage in the third stage (2004-2010) was the greatest among the three stages, and the variation range of node average circuitous coefficient of the counties along the Yangtze River and Hangzhou Bay was greater than that of the others because of the construction of Suzhou-Nantong Yangtze Road Bridge and Hangzhou Bay Bridge. 2) The node average travel time and the regional average travel time also got a great promotion under the construction of expressway in the Yangtze River Delta, especially in the outlying district of the Yangtze River Delta, while the variation range of node average travel time and regional average travel time would be decreased under the limitation of diminishing marginal returns of highway network construction. Through the comparison of spatial-temporal accessibility and its promotion in different development stages in the Yangtze River Delta, the necessity and significance of expressway construction are objectively demonstrated, which can be in favor of providing the theoretical reference for the transportation network optimization and regional development strategy formulation.