The rough shape, narrowness and safety issues along US 66 and similar highways in Arizona contributed to public sentiment towards rebuilding and improving safety along the state's highways. In 1954, President Dwight D. Eisenhower heavily endorsed the long-standing idea of constructing a nationwide network of four-lane divided superhighways. Originally proposed back in the 1930s, this system of nationwide freeways would have entirely controlled access through the entry and exit ramps, as well as grade-separated interchanges with other highways, roads, and railroads. The new freeways would also include smoother grades coupled with more gradual curves. These massive changes in highway construction were intended to help increase traffic flow and greatly reduce car accidents occurring on the national highway network. Eisenhower pushed the United States Congress to accept the idea and appropriate funding for the new system. Congress finally approved the proposal with the passage of the Federal Aid Highway Act of 1956, bringing into existence the Interstate and Defense Highway System. Several U.S. Highways in Arizona were chosen to become the corridors for the new Interstates, including US 66, which was slated to be replaced by I-40.