No it would level the playing field to some extent. The railroads build and pay for their own track. How many roads have the trucking companies built? Also it would allow more room for autos, cut down on fatal accidents, possibly lower insurance rates, and save on road repairs.
There is no subsidy. You and I and every truck owner pay for roads through gas taxes. The more gas you use (as in big heavy trucks that wear the roads out) the more money you pay.