Railroads are also enormously expensive to build and maintain. According to some reports a few times more so than motorways (at least in the UK). I don't know if there are technical reasons for rail to be more expensive but most railway organizations are inefficient monopolies. In other areas competitions drives costs down (e. g. drives inefficient companies out of the market) but railways are natural monopolies.
The decentralization helps. When you can call your mayor and complain about roads being in bad shape, you can get them fixed. Meanwhile, if there’s bad train service in your town, you might need an act of Congress to help you.
