The decline in U.S. passenger rail ridership didn't happen overnight. It's been a long term trend that follows the success of automobiles across a wide continent with plenty of open space.
Another factor is the tendency of larger businesses to locate outside the city -- producing the "Suburban Sprawl" you see in cities like Atlanta and Los Angeles.
Not only does this gut the inner city of jobs, but State and local governments are notorious for striking business development deals and tax breaks to bring corporations into a small cities promising "Jobs, Jobs, Jobs" which almost never materialize. This basically fleeces the local city taxpayer. But I digress.
A high interesting contrast between the U.S. and Japan is that the Shinkansen bullet trains compete very effectively with airlines for short- to mid-range business and tourist travel.
In America, by the time you drive your car to the airport, park it, pass through security, and wait 30 minutes to an hour to board your flight, taxi to the runway, and fly to your destination, a huge block of time elapses.
But to travel by Shinkansen from my Utsunomiya city (eastern Japan) to Kyoto (central Japan) takes only 4 hours with no security screening, boarding/deboarding times, or delays because the train arrives and leaves within 5 minutes on a very punctual schedule... and you jump aboard into a kind of business class seat. The fare is about $100 U.S. dollars (at current rate of 150 yen to the dollar).
And yet, the domestic airline business in Japan is also big -- the 4th largest in ridership of all nations. And so the longer range travel from the Tokyo area to western cities like Fukuoka, Hiroshima, Kumamoto, Kagoshima is where flying an airline is more time- and cost-effective.
Of course, America's airline passenger traffic dwarfs every other country in the world by a long shot.
So I've scratched the surface of comparing public passenger transportation in U.S. vs. Japan. When I get more facts, I plan to post a vanity.