If I were asked to measure productivity of railways I’d consider passenger miles per employee as a good start (or tonne miles for freight). Contrary to government propaganda, before BR was privatised it was reckoned as the most efficient railway in Europe, but I’m not sure who did the measuring and on what basis.
Having long stretches still controlled by men in signal cabins communicating via bell codes does not inspire hope in it’s productivity. Trouble is we are not good at investing in infrastructure.