Abstract:

In the Rapid Transit age, transportation accessibility has becoming one of the most significant factors of economic development. With the development of rapid transit, such as the highway and highspeed railway, accessibility of urban area is increasing sharply. Based on GIS and the methods of cost weighted raster analysis, this paper is conducted with regional accessibility indicators like average time, urban isochronous rings and daily accessibility to compare the accessibility spatial pattern changes of the central cities in Yangtze River delta with and without highway, with and without highspeed railways. Its purpose is to explore two types of rapid transit impact on central city accessibility. The result shows as follows. Firstly, highway network is perfectin Yangtze River delta, so the influence of the highway on city accessibility is relatively balanced, shortening the time between 30%-40%. Highway Bridges connecting both sides of the Yangtze River and Hangzhou Bay can significantly shorten the travel time of both sides, where the time variable ratio is high. Highspeed railway network is mainly along the megalopolis of the Yangtze River delta, so the changes of spatial distribution of the time variable ratio are unbalanced and accessibility improvement of the area along highspeed railway is apparent. The influence of the highspeed railway on the accessibility of cities which are along particularly the endpoint city like Nanjing and Ningbo, is more obvious than that of the cities like Nantong away from highspeed. Secondly, under the influence of highway, the expansion of isochronous rings is remarkable. Highspeed railway makes the isochronous rings stretched along the highspeed railway. Highspeed railway can better expand accessible area than railway within 1 hour. However, as a hub, the stops of highspeed railway are fewer. Only by upgrading other rapid transportation to enlarge the service range of stops, can it substantially expand communication circle of one day, reduce differences in external transportation between cities and areas around cities and promote the fairness of the social and economic development in Yangtze River delta. Thirdly, highway and highspeed railway can significantly optimize the daily accessibility between cities and speed up the formation of the regional division of the Yangtze River delta. The effect of the highspeed railway is significantly greater than the highway with 1 hour, but it tends to equilibrium within 3 hours, which is mainly due to the regional limitations of the Yangtze River delta. Highway can shorten total time of each city to other cities by more than 15 hours averagely, highspeed railway by more than 26 hours. Therefore, highspeed railway can better improve daily accessibility between central cities than highway. Lastly, although the benefits of Nantongs accessibility from the highspeed railway is small, in the future the electrification transformation of railway from Nanjing to Nantong will be completed, the time between two cities is shortened from 4 hours to less than 2 hours. When all the cities open the highspeed railway, the daily accessibility of all regional center cities in Yangtze River delta will be further optimized