Axles on railway cars are solid, making the two wheels rotate together even when they go around curves. So when they do go around curves, one of the wheels is dragged, thus making a loud screech. Also they lose a fair amount of energy in the process.
Is there any reason they can’t put differentials on rail car axles? I’m thinking about light rail and street cars[sup]1[/sup] rather than box cars and such. Would they save enough energy to make up for having to haul around the extra weight of the differential?
[sup]1[/sup]It’s possible that railed street cars already have differentials, but I know the light rail cars around here do not.