Public Transportation has to be the easiest way to move large amount of people. It has the added benefit of putting you in touch with people from all walks of life.
Updated
Thinking about this more, I keep thinking back to this idea that found the more lanes of traffic you add, the more traffic appears (as people get excited about the new road).
Public transit seems to be the most effecitve way to transit large amounts of people. I’m just not sure how to bring that to pass in a city like LA. Denver could be an example in how they used light rail to bring guests from their airport to the main city.