What major transportation innovation improved life after World War I?

The mass production of automobiles fundamentally transformed life after World War I by making personal mobility more accessible to the average person. Henry Ford's adoption of assembly line techniques allowed cars to be manufactured at a much lower cost and with increased efficiency, which significantly lowered the price of automobiles. As a result, a larger portion of the population could afford to own a car, leading to widespread changes in lifestyle and urban development.

The proliferation of automobiles enabled people to travel greater distances for work, leisure, and shopping, thereby expanding their social and economic opportunities. It also facilitated the growth of suburban areas, as individuals found they could live farther away from their workplaces and cities. The automobile culture that emerged during this time brought about a significant shift in American life, influencing everything from the economy to the infrastructure of roadways and highways.

Other innovations, while significant, did not have the same comprehensive impact on daily life during this period. Subway systems and electric trains were more localized modes of transportation and primarily served urban environments. Commercial airlines began to take hold later, but widespread air travel and its cultural impacts occurred after automobile culture had already established itself. Therefore, the mass production of automobiles stands out as the major innovation that reshaped society post-World War I.