The "affordability" of the automobile in the 1950s changed American culture.
Affordability is in quotes because the automobile manufacturers did something tricky. They got the US government to pay for the building and maintenance of roads.
So, unlike the train system where the train companies have to build and maintain tracks, the auto makers only had to make the cars.
This reshaped our country, allowing roads and cars to become the primary means of transportation in the country. In turn, people could then live outside of cities allowing suburbs to be created and fast food restaurants to be invented for people in the car on the go.
I think it would be the first answer because it makes more since
