You can literally buy derailers[1]. People will find away around this, making white paint useless. Engineers need to engineer.

1. https://www.aldonco.com/product-category/derails/

Derailers are common and are placed where people are working on tracks so a runaway car will go off the tracks instead of hitting the workers.

   Do NOT use where speeds exceed 5 m.p.h.

this is tackling regular natural derailment incidents not terrorism

OK, but a heatwave isn't going to buy a derailer