Yeah, it competes with road funding, but Amtrak also takes huge funding from the government, too... near 30% of operating expenses or about half of revenue:
Bloomberg: "After automatic budget cuts, Amtrak is getting $1.3 billion in taxpayer money for fiscal 2013, with $905 million of that going to capital costs and debt service, Kulm said. That’s less than the $1.4 billion the railroad received the previous year."
Amtrak: "In FY 2012, Amtrak earned approximately $2.877 billion in revenue and incurred approximately $4.036 billion in expense. No country in the world operates a passenger rail system without some form of public support for capital costs and/or operating expenses."
It may be a good social service, but it's a lousy business, and it is nowhere near self-sufficient.