The Federal Aid Highway Act of 1956 appropriated funding for the Interstate Highway System, to construct a vast network of freeways across the country. By 1957, AASHO had decided to assign a new grid to the new routes, to be numbered in the opposite directions as the U.S. Highway grid. Though the Interstate numbers were to supplement—rather than replace—the U.S. Route numbers, in many cases (especially in the West) the US highways were rerouted along the new Interstates. Major decommissioning of former routes began with California's highway renumbering in 1964. The 1985 removal of US 66 is often seen as the end of an era of US highways.
The Federal Aid Highway Act of 1956 appropriated funding for the Interstate Highway System, to construct a vast network of freeways across the country. By 1957, AASHO had decided to assign a new grid to the new routes, to be numbered in the opposite directions as the U.S. Highway grid. Though the Interstate numbers were to supplement—rather than replace—the U.S. Route numbers, in many cases (especially in the West) the US highways were rerouted along the new Interstates Major decommissioning of former routes began with California's highway renumbering in 1964. The 1985 removal of US 66 is often seen as the en.d of an era of US highways.