it was a limited consideration in the 50s, but basically bolted on the side of robert-moses-core with the odd rootcellar called "fallout shelter" as a marketing gimic in new developments.

round about 1:07 in everyone's favorite nuclear documentary is an example

That's actually not that new. I think that was part of it.

It is important to remember why cities were building highways through the fifties and sixties; why the federal government was promoting low-density suburban development and why companies were moving their corporate head offices to campuses in the country: Civil defense. One of the best defenses against nuclear bombs is sprawl; the devastation of a bomb can only cover so much area. Shawn Lawrence Otto wrote in Fool Me Twice[.]

https://www.treehugger.com/why-sprawl-was-caused-nuclear-arms-race-and-why-matters-more-ever-today-4854403