Figure 7

Testing the traditional gravity law with per capita GDP for the directed and undirected freight highway transportation networks constructed over five months. (a) Scatter plot of \(F_{ij}\) with respect to \((G_{i}/P_{i})(G_{j}/P_{j})/d_{ij}^{2}\) for the directed network. (b) Binning plot of \(F_{ij}\) with respect to \((G_{i}/P_{i})(G_{j}/P_{j})/d_{ij}^{2}\) for the directed network. (c) Scatter plot of \(W_{ij}\) with respect to \((G_{i}/P_{i})(G_{j}/P_{j})/d_{ij}^{2}\) for the undirected network. (d) Binning plot of \(W_{ij}\) with respect to \((G_{i}/P_{i})(G_{j}/P_{j})/d_{ij}^{2}\) for the undirected network