The Coach won't go

Today was 'Street Up' So empty from Bath Depot to Street. Nice drive out that way all across the Mendip's. Stopped at my usual lay-by to get my passenger list and set the destination etc. As I pulled away there was a noise which sounded like a flat tyre, but louder, much louder. The coach got slower, and stopped dead. It seemed like the brakes had stuck on. Contacted the depot and they said a replacement coach would be out to me within the hour. Finally got going in the replacement 55 minutes late. Apologies all the way to Bath. Change of driver here and after loading the passengers he got away 30mins late. Still haven't found what the trouble was. Rest of the day spent on the '17' bus around Bath. Off now for a week!!