Rail decay

[L. Spooner Inc]

In the real world, rails require constant maintenance. It might be interesting to create a mechanic with rail condition, where top-quality rails reduce train breakdown while poor-quality rails increase it. Maintenance vehicles would start as hand-pumped carts and develop into sophisticated, automated bots over time, and would operate out of depots. You could set them to automatically go and do maintenance on rails when they hit a certain condition.

[planetmaker]

Each railtype can have its own Infrastructure maintenance cost factor, thus can determine how much it costs to maintain it. Each vehicle has the same for running costs and its reliability decay which determines how quickly its state deteriorates and how frequently you need to service it to keep its probability to break down low. You can change the running costs, depending on what railtype it runs on. So is your suggestion already implemented (or rather can be done via NewGRF)?