Putting a solar roofs over any open-air carpark you happen to own is just a hilariously easier option. Hell, you could erect these OVER the train tracks.

https://greenox-group.de/photovoltaik-carport/ (Article is in German, but it's really more around the picture)

According to a completely un-sourced picture I found online, one carpark (in the USA) is typically around 5.5 x 2.6m, so if you had even 50 carparks on your site you could have ~715 square metres of panels. More, if you figure a way to cover the aisles between the rows of carparks too.

At the top end of all applicable figures (panel efficiency, solar irradiance, inverter efficiency), that could net you ~160kW at solar midday.

Now on the other side, standard-gauge railway is around 1.4m wide, and maybe you could cram a 1m width of panels between the rails.

That sounds like a lot - 1000 square metres per kilometre, and there are thousands of kilometres of railway lines out there - but it's harder to install, harder to service, gets dirty faster, is liable to get damaged, and now you have to figure out how to extract power from somehing a kilometre long, instead of an area that could be a square only around 35m (~115') on a side (for the above 50 carparks).

I know which one of those I'd want to run the cables for.

As has been pointed out many times when this dumb-ass idea comes up, only once you've exhausted every other possibility (carparks, rooftops, putting panels ABOVE roads/rivers/canals/cycleways/railways) and have literally no other viable installation locations, then we can talk.