Los Angeles its almost impossible to travel around without a car... Granted i didnt use the public system when i went over, only taxis... but the metro line is VERY small considering the size of LA, and to get from say, west hollywood (where i was staying) to Long Beach, you HAVE to go through Compton.... now i dunno about you, but being a nerdy caucasian english guy, i didnt really want to travel on that line...
in the US, it was a big plot to make public transport rubbish by the good ole folks at GM back in the 1920's... obviously with the oil farms in california the oil companies were up for making people buy cars too! [source]