Even if new capacity to absorb these new services could be made, it's still going to look like a real downgrade from a full rail service to a tram. And if the build quality isn't much improved on the M5000s then it won't be a lot of fun bouncing along the CLC
What advantages does the current rail service
actually have compared to a tram though?
It provides one faster train per hour, and stopper services that are somewhat slower than the tram service would be.
Ride quality might be somewhat better, but that is about it. And the tram provides access to the city centre in a way the existing railway simply does not.
Quite honestly taking a main line between two cities with long distance services and turning it into a bloody long tram ride seems counter-intuitive to me.
Is it really a main line for any reason other than tradition?
It's not the primary route between Liverpool and Manchester, it only carries two fast/semi fast and one stopping train per hour east of Warrington, all trains are formed of comparatively short DMU formations.
The primary stopping point for long distance trains on the line, Warrington Central, doesn't feature a non-CLC station (including Oxford Road and Lime Street as CLC) on its destination list until entry number 10 with Sheffield.
Sure it carries two longer distance services, but they hardly interact with much of the line other than stopping at Widnes, Warrington and sometimes Urmston.
Warrington Central gets 3 trains per hour to Manchester and thanks to the mess of the Castlefield corridor is highly unlikely to get more. The secondary statinos on the line get a service well below what would be expected for a peri-urban railway. One only gets one train per two hours but still manages 30,000 passengers per annum! I think there is probably an awful lot of suppressed demand on the route that could be released by more services, which we can only get by Metrolink-ification.
If that occurs, we can put many more trains down the line
and we can reduce the operational complexity of Castlefield by reducing the use of the current CLC access to a handful of freight trains per day. If and when Trafford Park depot gets relocated, even that would go away and the junction could be abolished entirely.
Wiring to route for EMUs sometime in the future definitely feels like a better solution to improve timings and reliability, and attract more business.
Wiring without improving the service frequency probably won't achieve much in traffic terms, and the service frequency can't be improved because of Castlefield.
The future without Metrolink is BEMU services on the present pattern, most likely for the forseable future.
Wiring it would be an enormous expensive for the gain at present 25kV prices.
As with the CLC, I don't see the point in running all the way out into Northwich (and what about services beyond to Chester?). Whilst an increase in frequency would be marvellous, the same concern about ride quality exists as with the CLC. It would be a full hour sitting on a tram every day for commuters, and as bad as the 15xs can be, they are still way more comfortable than the M5000s currently working Metrolink. And once you break out of the cover of the urban sprawl, you'd notice this a heck of a lot more, the wind out here is almost as bad as it is in my old haunt in West Yorkshire. So without some pretty high specs for any tram-trains, I'd again I'd argue that it would be a downgrade that won't attract new custom, which is really what should be a priority for Metrolink.
The experience from Germany is that people are willing to spend this long on tram/tram-train vehicles out in the sticks.
Karslruhe even puts people onto tram-trains for ~90 minutes. The Karlsurhe S-bahn line S8 is notionally 120km long!
Running through to Chester is a bit far even for me, so I'd suggest breaking the services at Northwich. The journey planner seems to favour going via Warrington Bank Quay or Crewe most of the time from Manchester in any case.
One train per hour to Piccadilly or four/five tram-trains per hour. (The heavy rail solution is going to be fighting larger flows for paths over Stockport Viaduct for the forseable, so unlikely to see that second train per hour materialise)