One thing railroads (outside the NEC) are now using solar power (and batteries) for their signals.

The signal equipment railroads use varies considerably.

One of the most interesting tours I was ever on was to go through the CSX signal shops in Savannah and they have to be able to repair any kind of electronic equipment on the railroad and some of the electrical instrumentation they use belongs in a museum (think vaccum tubes!)

Edit -- I'm just back from a trip where we saw wind power being used to charge batteries for signals. (Think old fashioned farm wind mills !)

Bob H