So where would the extra WCML paths come from for the freight trains to get to Northwich via Sandbach instead of Northwich via Altrincham?
There's more freight than just the 'ICI' freight. Here's today's booked freight paths through Altrincham:
http://www.realtimetrains.co.uk/sea...1/26/0000-2359?stp=WVS&show=freight&order=wtt
The journey time was recently slowed down by around 3 minutes. The reason being loadings at Northwich, Knutsford, Hale and Altrincham are generally very high for a service which is just hourly using vehicles which only has 3 or 4 passenger doors to board/alight through. As there isn't the stock available to run longer trains or more trains the journey times had to be extended instead.
If there were multiple services some would miss out the smaller stations. When the tram-train case for the Mid-Cheshire line was being examined they came up with following assumptions:
A class 170 operating Altrincham-Greenbank would take 27 minutes stopping at all stations or 23 minutes if 2 stations were missed out.
A new 50mph tram-train operating Altrincham-Greenbank would take 25 minutes stopping at all stations or 23 minutes if 2 stations were missed out. Of course, if you try to fit 5 tram-trains an hour around the freight some services won't run at the fastest possible journey time.