The Safety and Comfort of Passengers

A sales rep stops his company Vectra to eat a pie in Kirkcaldy, and a story comes on the radio about an old guy who taught him to drive a bus. The instructor's had a bad accident, and although the cause seems obvious, the sales rep suspects other reasons. As he reminisces about his time as an Edinburgh student, driving buses in the summer holidays, he recalls some unsavoury events; for instance, how did his clippy know the provenance of a turd on the upper deck...?