I have no idea why the line speed is 25mph but this could simply be reduced maintenance on a currently freight only line to save money.
A round of tamping could improve line speed without the need for extensive relaying.
A quick flick through the sectional appendix shows:
- Line is currently passenger rated throughout from Sandbach to Northwich West Jn
- 20mph throughout (inc. Middlwich Loop) except 15mph through the loop just north of Sandbach (both ways) and 10mph at Northwich South jn until it joins the Mid-Cheshire Line
- 8 Level Crossings (6 UWC, 1 FP and 1 UWC/FP).
- Down & Up East Chord to Northwich station is 10mph Non-Passenger rated, feeding into the 15mph non-passenger rated Down and Up Goods at Northwich Station.
- Pointwork at Northwich East Jn is all 15mph to/from the DUG.
The branch itself is c.8.5 miles long, the current all-stopper journey time from Manchester Piccadilly to Northwich is 54 mins. Given it's only really Middlewich being served better, what does the journey time over the branch need to be to offer an effective service to the town?
Google gives 8 mins to drive from Middlewich to Sandbach station, probably needs to be 5 mins then between stops. 3.75 miles in 5 mins = average speed of 45mph. So we're talking tripling the existing linespeed from 20mph to 60mph, which after allowing for the things like acceleration, decelaration, curve at Sandback etc, give you your 5 mins.
That would then give your 4.75miles from Middlewich to Northwich @ avg.45mph = 6.5mins so 1h from Middlewich to Manchester Piccadilly. (Google says 40-50 mins driving on a clear day from Middlewich to Manchester Oxford Road NCP).
Not bad, but not going to be 'transformational' modal shift.