The average company in the US pays an incredible amount of corporate tax.
Do away with that stifling influence, and the rails would thrive.
Is it considered a 'subsidy' if it is simply the absence of murderously high taxes?
Look what happened to e-tailing and e-commerce in general, helped in part by absence of taxation on internet transaction.
The central lesson is, don't tax it, and if it is remotely feasible, in the United States of today, it will thrive.
The railroads pay property taxes on their rail lines and facilities, to include the train stations. The airlines don't have to worry about that expense in relation to airports.
The government has a nasty tendency to penalize success.