Figure 1

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