Heralded a new industrial system based on assembly line methods and mass-production techniques.
Sprang an enormous industry into being, with Detroit becoming the motorcar capital of America.
Ford was able to utilize assembly lines and standardization (see Fordism!) to produce a vehicle for about $260 (affordable for a thrifty worker)
By 1929 and the start of the GD, 26 million motor vehicles were registered in the US → far more (proportionally) to any other country in the world.
The new automobile industry displaced steel as kingpin and employed 6 million people. It was a major wellspring of the nation's prosperity and created jobs in other industries (rubber, fabric, glass, etc.)
The US's standard of living rose sharply.
New industries boomed (petroleum, oil) while older ones suffered (railroads)
Speedy market of perishable food, prosperity for farms, nation quickly constructed roadway system.
America developed further suburbs, became a country of commuters to work, school, and church.
Safety was an issue. There were a LOT of automobile deaths in the 20th century.
Motorcars came to be seen as a necessity and a sign of self respect. People could use them to travel more and transform their leisure time, and cars also provided women with more independence from men.