That’s the consequences of not maintaining it, rather than why it costs.I would have thought that would be obvious.
A small pothole on a main road is annoying. If it is a really bad pothole and you are unlucky in how you hit it, you might get a puncture or you might, worst case scenario, damage your suspension or your steering arm.
The equivalent of a small pothole on a railway line would see an express train flying off into the scenery at a very high speed.
But back to the point of the thread. Unless costs are reduced or government decides to increase net subsidy then revenue has to be maximised. The peak/off-peak split appears to do this. Scotrail’s trial was revenue negative as passenger numbers didn’t increase enough to cover the lower fares.