Spatial accessibility plays an important role in urban development and has been a prerequisite to the linkage and development of regional integration. Taking Wuhan metropolitan area as an example, we built a series of accessibility models based on geometric and topologic distance. The proposed models are then applied to examine the spatial structural properties of the road network of Wuhan metropolitan area. It is found out that: (1) there is a high uniformity and consistency between the entire development level and accessibility pattern of the road network of Wuhan metropolitan area; (2) significant spatial differences are detected in the road network, i.e., distance decay and spatial constringency for the entire road network; (3) thus, the network shows an obvious grade-layer structure and core-periphery structure; (4) but high-class road network evolves unevenly, which causes the asymptotic deformation of the circles represented spatial-temporal accessibility, with the result that the total structure has a "Y-shaped" pattern from northwest to southeast; (5) the spatial distribution pattern of the topologic accessibility of the road network are scattered, and some skeletons and axes can be found, which results in the "axis-spoke" style and "fish spur" shape of the whole road network.
The above structures and patterns of the road network have a great impact on the transportation system of the city. For instance, some roads with very low accessibility are easy to have traffic jam and low efficiency for distributing traffic flow to the entire road network; some skeletons such as the east-west roads along the Yangtze River and the north-south roads along the Beijing-Guangzhou Railway have been very important to accommodate the traffic flow of the entire road network. We also found that the spatially uneven accessibility pattern of road network has a close relationship with the city and town system, transportation facilities and social-economic development of the area. It should also be noted that there is a complex reciprocal-coordinate relationship between highly developed road networks.
Therefore, the metropolitan area should pay more attention to the construction of transport infrastructure, especially those high-grade traffic lines and joints, because they are propitious to the servo and validity of road network; secondly, we should better develop some secondary cities in order to form a multi-polar structure of road network, which could enhance the balance and stability of total road network; thirdly, the construction of regional expressway network should be strengthened in order to promote the operation level and efficiency of road network.