...Not sure about planes, but according to Subsidyscope we drivers only cover 51% of the Federal outlays for the Interstate Highways via the Federal fuel tax. Amtrak on the other hand between fares, state fees, contract services, rents, interest, etc. covered 69% of it's 2010 budget; leaving 31% for the Fed to pick up.
First, I think you are misreading the report. The 51% figure is for all highways - interstate though local streets - not just interstate, and the taxpayer support is for all government, federal through local, not just federal. Even the 51% figure is somewhat bogus since about 25% of the federal fuel tax revenues are diverted to non-highway uses, including rail. If all federal fuel tax revenue went to highways, the payment rate is over 60%.
Second, highway users pay 100% of the costs of their vehicle, insurance, maintenance, license and registrations fees, and fuel. If you or I drive 100 miles, we pay over 95% of the total cost of that trip. Amtrak users pay about 69% of the total cost of their trip, and less if you add in state support subsidies. To equate 51% support of highway infrastructure only (with the rest 100% paid by users) to 69% of all costs for Amtrak, is apples and oranges in the truest sense.