Although the limitation to 540 central offices required the most populous states to be divided into multiple NPAs, it was not the sole reason to subdivide a state. An important aspect was the existing infrastructure for call routing, which had developed in preceding decades independently of state boundaries. Divisions also attempted to avoid cutting across busy toll traffic routes, so that most toll traffic remained within an area, and outgoing traffic in one area would not be tributary to toll offices in an adjacent area. As are result, New York state was initially divided into five areas, the most of any state. Illinois, Ohio, Pennsylvania, and Texas were assigned four NPAs each, and California, Iowa, and Michigan received three. Eight states and provinces were split into two NPAs.