To those of us who don't live in NYC, the gain is not so clear.
The context is all different: when I lived in NYC, I rode the the subway all the time. But I also walked home on nice days; I worked midtown, lived downtown. Now that I live in Berkeley and work in San Francisco, that kind of thing is infeasible. There are a few cities that grew up before any kind of transport was popular and thus made the transition to public transit; but the rest of the US just isn't layed out that way.
Patrick mentioned the idea of shifting the highway subsidies from trucks back to railroads; Patrick: do you still live in the Bay Area? That would be disasterous for the west coast, since the rail lines can't handle anything near to what the highways can in terms of capacity, speed, and flexibility. If you look at the I-5 corridor (roughly Seattle to San Diego, including Portland, Sacramento, San Francisco and Los Angeles), you'll mostly see mountains. And 32MPH railroad tracks. It's just not the right answer for that kind of geography.
/jordan