Fully agree with the above. A simple east-west bypass tunnel for inter-city/fast trains makes a whole load of sense. Finally lets the core routes and stations in Central Manchester be used optimally (S-bahn style core.)
Such a tunnel that isn't reliant on HS2 also means much shorter platform lengths (and therefor stations) means the mooted underground station at Piccadilly would only need be half the length and width of the Old Oak Common HS2 station, making the whole thing a much more realistic prospect. There's also opportunities for a secondary station in east Salford to fully relieve Castlefield by reducing the number of "feeder" trains into Piccadilly for passengers to reach the new line, as well as providing fast and convenient connections to Media City and North Manchester. The site is brownfield with multiple rail lines crossing it, making for the perfect interchange and prime for transit-oriented-development to help fund the project.
This is all show in think tank "NorthOnTrack"s "CrossNorth" plan below:
View attachment 153327
To start you'd be able to run 8tph through it assuming a turn back facility east of Salford Interchange for 2tph. Once connected to a new, segregated link toward Liverpool/Warrington that can be increased to 10tph all through-running.
Also, unlike previous NPR plans, it actually connects Sheffield, Chester & North Wales to create a true "CrossNorth" network, fully relieving Castlefield of all inter-city services.
In terms of airport connections, as mooted by the posters above, with the existing network free to run S-Bahn style, you'd get metro-frequency services to it from Piccadilly, a trip no longer than 20mins, and finally using the densely populated "Styal" line through South Manchester for local services, rather than a "sink" to turn inter-city services around at the airport due to lack of west-facing terminating capacity in Central Manchester.
Seems like a win-win to me personally, although I understand everyone will have their own views on this one. The Manchester problem has always been somewhat controversial!
Marshy.