Well mechanical things in San Fran and CA in general tend to be of better health than their east coast brethren due to differing climates. (Think of all the still sweet condition classic cars out west.) But the true reason for San Frans seriously spiffy trolly fleet is that that are in themselves a serious tourist attraction. When you think of San Fran you tend to think of the trolly, sourdough and the markets... or hippies! So the city spends a lot of cash keeping them in tip top condition, but if you google enough you can find examples of them breaking or of serious accidents there.

__________________
"i live my life in the city"