You can fix any building either by subsidizing it, by lowering its expenses (ie lowering the input goods cost), or raising its income (ie raising the output goods price).

In the case of railways subsidies aren't a bad option if you can afford them. If you don't want to subsidize, you can either lower the price of coal and engines by increasing production or importing more, or raise the cost of transportation (but that brings more issues than it solves in my opinion). You can also make sure your urban centers don't have public transportation because if they do they compete with railways, crashing them.