The biggest issue with public transit in LA for commuting is the last mile problem. It's similar to the "last mile" problem of fast fiber optic cables to slow copper wires to homes. Here the issue is efficient and fast rail transit to extremely inefficient bus system for that last few miles from stations to work. I once tried to plan my commute using public transit and here's what I found:

1) Drive to rail station for park and ride? About 10 minutes, great.

2) Light rail to station nearest to my work place? About 30 minutes and covers 90% of the distance, awesome.

3) Station to my work place? About 1 hour using bus system...

I'll just drive instead since even with bad morning traffic I'll still get there faster because the bus system is really really bad.

I get a bit upset when I think about it because I can get there 90%, but that last bit is ruined by the stupid bus system.