> The problem in most of the US is that you have a big congested highway, and then you get off the highway and drive another five or ten minutes on side streets to your destination.

> there aren't regular buses on the side streets because there isn't enough traffic there to justify them

That is the usual problem. But it's usually possible to have freeway buses connect to local buses that drive around an area. Driving around nearly empty buses might seem like a bad idea - but it's the best idea there is when people aren't in a car (because they just jumped off the train or freeway bus). A second solution is having people drive a short distance on local roads from their home to a public transit hub such as a train station, if there is no bus to take them near their homes - The problem is that once you get off a train or freeway bus you might not be at your destination. But that's where public transit can't solve the problem. Zoning and building also needs to change. Without that, people might still have to walk 30 minutes to the office.

The situation where a company puts up an office with a large parking in an "office park" (or whatever it's called) which might be 15 minutes from the closest public transit is the root of the problem. Since people have to use the car to their office anyway, they wouldn't be using the bus even if it existed, as you point out. So the solutuion has to be in both ends: offices and housing needs to be in denser, more walkable areas, for example. I don't think the traffic problems in LA can be solved without fundamentally changing how and where people live and work.