The gross number of derailments isn't very meaningful, what you need is the derailments per train-miles-traveled, analogous to the collisions per vehicle-miles-

The gross number of derailments isn't very meaningful, what you need is the derailments per train-miles-traveled, analogous to the collisions per vehicle-miles-traveled that is used for road safety. If we're running fewer trains, obviously we should expect fewer derailments. As some other commenters have noted, it might be even more useful to get the total weight of derailed cargo, per (mass times distance), I suppose.