The Eastern Seaboard and California are fairly dense and have TERRIBLE traffic congestion and pollution problems. A high-speed train from Boston to Atlanta and from San Diego to San Francisco would help a lot of that, though fixing public transit within the cities would help even more.

I HATE driving on 95 to get to my family's place. There are always accidents, and once you hit Fredericksburg, VA, you're in slow or stopped traffic thanks to the DC-NoVa mess. If Amtrak weren't utter bollocks, I wouldn't have to.