Overnight trains often get diverted due to works. For example, one night last week a train I was on went from York to Leeds via Sherburn-in-Elmet, Milford Junction, Castleford and Methley Junction. (change ends). Then normal route via Dewsbury to Huddersfield. (change ends). Then via Bradley Wood curve to Brighouse, Milner Royd Junction, Hebden Bridge, Manchester Vic, Salford Crescent (change ends) then back to Piccadilly and the Airport from there.
Having all these routes is handy. Only last week also a Northern unit failed at Ashburys so my Liverpool to Scarborough train changed direction at Piccadilly, went to Salford Crescent, changed ends, then back through Victoria then to Stalybridge via Ashton-U-Lyne. We were only 30 mins late at Stalybridge - and as we left Piccadilly a good 15 - 20 mins late we didn't do too badly.
TPE Crew no longer sign via Bradford Interchange, so that route is not an option. It came in handy in 2007 though when there were the floods at Mirfield when Northern cancelled many of their trains to allow TPE services to go via Bradford (stopping at Halifax instead of Northern).
Daytime diversions generally follow the same pattern on the North Route - Sundays between September and December for all or part of the day trains generally go via the Calder Valley. ON Sundays around February for all or part of the day trains between Leeds and York generally go via Castleford.
