Cities are divided into local governments responsible for local commuting infrastructure that is used by both their residents and outsiders. In this paper, I study how metropolitan fragmentation affects the provision of commuting infrastructure and the distribution of economic activity. I develop a quantitative spatial model in which municipalities compete for residents and workers by investing in commuting infrastructure to maximize net land value in their jurisdictions. In equilibrium, relative to a central metropolitan planner, municipalities underinvest in areas near their boundaries and overinvest in core areas away from the boundary. Infrastructure investment in fragmented cities results in higher cross-jurisdiction commuting costs, more dispersed employment, and more polycentric patterns of economic activity. Estimating the model using data from Santiago, Chile, I find substantial gains from centralizing investment decisions. Centralization increases aggregate infrastructure investment and population. More importantly, for a given amount of investment, centralization yields large welfare gains due solely to more efficient infrastructure allocation.