While the discussion here is regulation of interstate commerce, state lawmakers can use a provision in the legislation creating the FRA that limits federal preemption of safety standards for a unique local safety hazard.
After Canterra Loop the California PUC tried to mandate State standards for things like track engineering standards, wayside detector spacing, employee training, train make up standards and accident reporting. Cal PUC identified 33 unusual conditions based on grade, curvature, proximity to sensitive areas, etc. Their novel approach failed in court when railroads identified 33 similar or even more adverse circumstances outside California.