(29 Oct 2023, 12:04 am)mb134 wrote There really aren't always spares available. The spare vehicles on paper are there to cover for things like planned maintenance, MOT, breakdowns etc., there isn't 10-12% of a depots PVR sat around every day on the off chance a service is late. 

Sometimes depots might be in a position where they have a couple of fully spare vehicles per day, in which case they might use them to regulate service. In terms of flexibility though, it's likely easier to keep them at the depot so that engineering can take them to a breakdown quickly. 

Essentially, if you're parking up buses in a bus station with the sole intent of replacing late running 56s, they should be part of the PVR for that service if the service cannot reliably operate without them. That is what increases the cost.