Modeling phase changes of road networks

Adopting an agent-based approach, this paper explores the topological evolution of road networks from a microscopic perspective. We assume a decentralized decision-making mechanism where roads are built by self-interested land parcel owners. By building roads, parcel owners hope to increase their parcelsÕ accessibility and economic value. The simulation model is performed on a grid-like land use layer with a downtown in the center, whose structure is similar to the early form of many Midwestern and Western (US) cities. The topological attributes for the networks are evaluated by multiple centrality measures such as degree centrality, closeness centrality, and betweenness centrality. Our findings disclose that the growth of road network experiences an evolutionary process where tree-like structure first emerges around the centered parcel before the network pushes outward to the periphery. In addition, road network topology undergoes obvious phase changes as the economic values of parcels vary. The results demonstrate that even without a centralized authority, road networks have the property of self-organization and evolution; furthermore, the rise-and-fall of places in terms of their economic/social values may considerably impact road network topology.