长江下游地区过江通道发展利用与“时空压缩”的演变特征

长期以来过江通道供需矛盾突出,高效利用现有通道并合理规划建设新通道设施、吸引两岸要素无障碍流动成为长江下游地区率先实现跨江发展、推进次区域合作的基本物质保障。基于此分析2000年以来长江下游地区公路过江通道建设对南北岸间交通的“时空压缩”效应,尝试探讨高等级公路网体系中过江通道通行利用空间特征。研究时段内过江通道建设实现由点到面扩张,从单一到多样化的跨江条件改善压缩区位差异对发展造成的不公平,跨江时间成本逐渐转变为自岸向两侧的由高到低梯度推移。沿岸地区就近选择过江通道,中远岸市县由高等级公路网引至特定通道方向,完整的过江通道是包含跨江桥隧和后方高等级连接公路的交通走廊。各通道因其在路网体系中的定位不同,通行利用存在差异,区域空间和基础设施建设的有限性要求建立“干线公路-跨江桥隧”多对多选择,提升既有通道通行能力并将连接道路建设向新通道方向倾斜,以分流通行压力并缩小区域内跨江成本差距。

Development and spatio-temporal evolution of cross Yangtze highway passages in the lower Yangtze region

For a long time, the contradiction between supply and demand of cross Yangtze highway passages has been prominent. Making use of existing channels while rationally planning and building new channel infrastructures, which aims at attracting barrier-free circulation of elements has become the material basis to promote the development of cross river integration and sub-regional cooperation in the lower reaches of the Yangtze River. In this article, we analyze spatio-temporal effect on river-crossing transportation development since 2000, which is caused by the construction of cross Yangtze highway passages in the lower Yangtze region. Also, we attempt to explore the location difference and spatial characteristics of utilization among passages in the high grade road network system. By the end of 2016, the number of crossings of the Yangtze River had increased from 4 to 17. The average cross-river time of cities and counties had decreased from 7.92 h to 5.75 h. The time cost of river crossing rises in line with the shore distance, showing a little ups and downs in the process. The amplitude of cost increased slightly larger in the south than that in the north. The cost reduction rate from 2000 to 2008 was higher than that of 2008-2016. The construction of the passageway was expanded from point to surface, which enables more cities to enter the river passages within a reasonable amount of time. Cross river accessibility pattern had gradually changed from a radial structure centered in Nanjing to gradient transformation from the shore. From 2000 to 2008, high level of time compression occurred throughout the region, forming a traffic oriented mode. From 2008 to 2016, there was a slight cost reduction, but the difference in cross-river time cost in the rear area was amplified. The edge of research area remained a high level of decline which had inherent weakness of channel access. The condition of river crossing changed from single type to diversity, and the development chance for the compressed rear area was unfair, due to locational difference. With the increasing number of channel, their utilization became different. Nanjing, the hub node of river crossing in the lower Yangtze region, supports all directions of river crossing transportation using gradually improved radial high-grade highway network. Jiangyin Bridge is responsible for river crossing from the north to the south in the east part of the research area and shore area of Jiangsu province. Its unique high-grade highway network seamlessly guides the use of remote cities and counties. Wuhu Bridge and Tongling Bridge are the first bridges which jointly undertake the responsibility of river crossing in Anhui province. Subsequently, Anqing Bridge serves as the passage between cities on the west bank along the Yangtze River in Anhui province and most cities on the south bank as well as the central and north parts of Anhui. After 2008, only the Wangdong Bridge has acted as a leading role in the river-crossing transportation of north-south and northeast-southwest of the study area. In addition, the areas along the Yangtze River have been affected greatly thanks to the most direct improvement of river-crossing condition made by the new passages. With the increasing distance from shore, it is more likely to have access to the passageway quickly. Through the high grade highway, cities in a certain range can be linked to the direction of the specific passage, forming a "confluence" structure. It can be concluded that a mature and complete passageway should be a transportation corridor that includes a bridge over the river and a high grade link in the rear. The disparity of utilization originated from the difference in the positioning of each passage. Because of regional space and infrastructure construction limitations, networked efficient transportation requires establishing multiple paths to reasonably distribute river crossing in the process of advancing to the coast. "Many-to-many" river-crossing selection between passages and trunk highways can be finally formed in order to improve existing passages' traffic capacity and divert cross-river traffic pressure.