Congressional passage of the Federal-Aid Highway/National Interstate and Defense Highways Act of 1956 was instrumental in establishing a nationwide network of modern freeways. Originally designed for military purposes, this system would have huge impacts on civilian transportation as well.
The 1950s and 1960s saw the greatest amount of national and state highway construction. This even included a fantastic proposal to use atomic bombs to excavate a highway route through mountains!
California launched its own ambitious program. Some of these new freeways cut through the heart of many of the State's cities and towns, destroying many older neighborhoods. The “Freeway Revolt” of the 1960s saw some cities call a halt to such projects.