I've been in a discussion with some family members who traveled around the world and examined the differences between Americans' preferred mode of transportation and many other countries'. As far as I know (and I've been to most of the U.S. states), Americans like cars even in crowded urban places like Los Angeles and San Francisco, perhaps except New York City where its public transportation really thrived. In countries like Japan and many European countries, public transportation is the main mode of transportation, particularly subways and trains. Is there some historical explanation for this cultural phenomenon, perhaps in the way the American automobile and railroad industries developed? And how would it compare to countries that prefer public transportation?
Some others may have better experience with this topic; I'm a film historian, and have looked at car culture largely through the drive-in theaters of the '50s and '60s, so my knowledge is admittedly skewed, and I'm only going to tackle your first question.
American car culture really exploded after World War II, for a number of reasons, but two are perhaps the most important:
Some other factors: leisure time and leisure activities became more common phenomena, so people also did more traveling -- whether driving to the beach for the day or taking more substantial vacations.
And the Baby Boomer generation was the first to grow up in this car culture: for the first time, teenagers could take the family car and drive to the malt shop, to the drive-in theater, or simply cruise about town. This made car culture especially vital for Baby Boomers. For their parents, cars were functional; for them, however, cars were freedom. They allowed teens to be amongst their friends, free of parental oversight (and perhaps not coincidentally, this was also the time when teens were first being widely recognized as a separate demographic between adult and child).
It wasn't an organic transformation. The federal government wanted to get white middle class people out of the city. The federal government spend billions on highways and grants and loans for suburban homes. This meant sprawl and anti-public transportation. Even today riding the bus has a huge stigma. It is sad because this short-sidedness is why our infrastructure and public transportation is second world. While Europe and East Asia built intercity rail and large subway systems, the US abandoned it. If you look at old pictures before or during the second world war, streetcars and inter-city rail were popular-- and not just for the poor.