Scheduling for failure

Christian Wolmar writes about the romance of the rails in My window on America: From Los Angeles to New Orleans on an epic rail adventure:

“Then in the dark, we broke down, and the lights went off. The conductor said a hose has come undone and that the power had to be switched off while the problem was examined.
They had to send for an engineer, who arrived quickly with a huge lamp that eerily lit up the scene and solved the problem.”

There was more excitement and evictions at San Antonio, which we reached at 9.30pm and where we were scheduled for a two-hour stop. It gave us time for a drink in a bar. A couple of girls on the train, heading for a music festival, had drunk too much, and were too out of it to stop singing on the way back to the train, even after a conductor warned them to stop. The train was delayed for the police to be called. Off they went, still intermittently singing and swearing, into the cooler.

The train meandered around the outskirts of New Orleans, but still arrived an hour early.”

So the train broke down once and had to have the police called, but it was still early. How much slack is built into the system to ensure on-time arrivals?