Which non-electrified routes are the shortest on Northern's network?
 

The reason I'm asking is because I'm aware that trains such as Southport to Rochdale/Manchester, Chester to Manchester via Stockport and Sheffield to Manchester (local) use Pacer 142s (with journey durations of approx 1hr30) Yet there are shorter journeys using 150s and 156s.

However, Northern aren't as bad as First North Western who did on occasions use a 142 on a Manchester to Holyhead route and on a daily basis used a pair of 142s to run an afternoon Chester to Blackpool North service, which has since been spilt in to two seperate services.

First North Western were unpredictable in which trains they would run on which service expect for the 175s.

Regarding the 175s I don't know why they were put on the Manchester Airport to Blackpool route as opposed to the Buxton to Blackpool route which is a longer route and more overcrowded. However, I'm aware the 175s are now with Arriva Wales so it can't be changed now.