Switzerland turned its train tracks into solar power plants

I agree.

This addresses one of two main failure modes of solar roadways (grippy coating disintegrating from being driven over), but keeps another one (contamination).

Note that this particular trail was right next to a terminus of very lightly used branch, served by well-maintained rolling stock.

Should one install this anywhere with large traffic of older locomotives, panels will quickly get covered in dark goo from oil drip+dust, reducing output dramatically.

Are the cells themselves tougher, or do they just depend on the frame to keep them safe? Just navel gazing, but I wouldn't be surprised if these had better ROI- for conventional solar installations, the mounting hardware can be significantly more expensive than the panels themselves. And you have to worry a lot more about things like wind. Off ground would have better performance in winter, but shorter days in winter are going to be lower outut regardless

Also less grease dripping down on them, less water pooling on the flat surface...

My first thought was the sound barriers along the tracks and highways. A bit too small surface area and angles but looks like the panels are quite effective nowadays so with a some form of kinetic/hydro battery you can have an almost free lighting along the road for a useful life of the panels.

No need to worry about that: Switzerland is a developed country, so it has a functioning welfare system. Nobody has to steal solar panel to survive.