With the rapid expansion of transportation corridors in extent and density, the ecological effects of road networks also have become increasingly extensive and intensive. A number of recent ecological studies have investigated the structure and spatial pattern of different kinds of road networks and their various effects on biodiversity and ecosystem functioning on local and regional scales. Attempts have also been made to explore the ecologically optimal structure of road networks. This paper examines the impact of road networks on the natural environment in Zhejiang Province and provides several suggestions for developing an ecologically optimal transportation network. First, we introduce the road network theory, particularly the two theories proposed by R.T.T. Forman and J.A.G. Jaeger, respectively. Then, we use Forman′s theory and the minimum buffer width method to analyze the fragmentation effects of different types of road systems on forest ecosystems in Zhejiang Province. Our results show that national and provincial roads cut through and took up much space in forests, causing severe impacts on the ecological functions of forest ecosystems. Highways also seriously fragmented the forests and reduced the native biodiversity. We project that, at the end of year 2020, the network of national roads, provincial roads, and highways will cause even greater damage to the forest ecosystems if no measures against this road encroachment are to be taken soon. Finally, we propose five specific ways of improving the development of road networks in Zhejiang Province.