Transportation infrastructure projects organize mobility and land-use development across metropolitan areas. As such, they are typically undertaken by states, regional governments, or public authorities overseen by higher-level governments. But since these projects have localized implications, city governments have an interest in shaping project planning.

In this journal article, I examine case studies of six rail transit projects in France and the United States to understand the regional politics of infrastructure investment. I show that even when deprived de jure jurisdiction over planning, the local governments in these case studies harness the broadly shared view of their democratic legitimacy to exert de facto power over matters affecting them. These localities increase their power through intermunicipal alliances composed of cities whose residents hold contrasting ideological viewpoints. These alliances are founded on mutual deference, which means an agreement to support—or at least not oppose—the perspectives of neighboring localities if doing so does not threaten a locality’s own needs.