Indeed - you would have thought that all the drivers Saturday leave would be agreed up front at the start of the year so the situation on being reliant on overtime would not arise.
Most train crew annual leave is rostered into pre arranged blocks for exactly that reason: predictability. Non rostered “ad hoc” leave can be requested but can be denied in certain circumstances (at my depot there is a quota of three who are guaranteed it each day, on a first come first served basis. Anyone lower than three will simply have the request declined if their work cannot be covered).
There is always a element of unpredictability as to how many drivers will be available each day. If someone goes sick, or has an incident and is taken off track, their work has to be covered until they resume. This is done using spare drivers (ie drivers who rostered to work that day, but not allocated a job), failing that rest day work volunteers, or “standby” (who are rostered to sit in reserve in the depot) as the last resort. Standby is used last as they’re the last line of defence against cancellations, and once they’ve been used they’re gone.
Then there are other restrictions: even if you have volunteers rest day work can only be allocated in accordance with requirements to have 12 hours between shifts, the fatigue index etc. Spare drivers have a maximum agreed movement (which varies) and cannot be allocated anything outside their rostered times +\- movement. Movements off spare need to be posted up within agreed timescales (72 hours at our place) And of course it goes without saying the crew need to sign the appropriate routes and traction!
When all the above has failed, that’s when you get down to crewing ringing round asking people for favours, often for a sweetener. The success of this depends entirely on goodwill, whether people have made plans etc.
In short, it’s a complicated business!
