How did cars change American life?
If you put 1900 as the start date of automobiles, it wasn't but the date is convenient and not far off, then all travel prior to 1900 had to happen relative to the schedule of a train, streetcar, stage coach, or via the use of your horse or your feet. Regardless, each imposed limitations on the ability of any American to travel to any destination.
The introduction of the automobile of course changed all that. Prior to 1900 even the wealth were captive to the train when traveling long distances. The introduction of the automobile gave them the immediate advantage of travelling at will. And once mass production was put into play, the inexpensive automobile became a possibility for all Americans.