I don't think the problem is going to be gradients. Modern electric stock can work pretty steep gradients.
Basically though the main point to bear in mind is that it will not be possible to use the existing Cowlairs tunnel in any cross city scheme. The station throat at Queen St is too tight and you couldn't get down under George Square quickly enough there, gradients would be a problem.
So any cross city tunnel will need a new portal in north Glasgow.
I can see about 5 different options:
- Just to the south of the Cowlairs south curve, east of the existing E-G track.
- Just to the north of the Cowlairs south curve between the existing E-G track and the Network Rail maintenance depot.
- Somewhere around the Eastfields depot area.
- Somewhere around Barnhill / Railcare Springburn with access to both the Cumbernauld and Springburn (for E-G) lines
- Somewhere around Bellgrove with access to the E-G line being via Springburn.
If you were looking at a pure single station cross city line then Option 1 is probably the best and would allow access to Cumbernauld, Maryhill and Croy services.
Option 2 would lose access to Cumbernauld, Option 3 would lose access to Maryhill & Cumbernauld and Options 4/5 would have a journey time penalty compared to options 1-3.
If you were building more of a Metro style system with 3-4 underground stations then the other options might have other advantages and if a future High Speed Rail station were located at Bellgrove then there would be a logic to serving that location.
One thing all versions would likely have in common would be that they are only likely to serve one out of Central or Queen St (almost certainly Central). The 2 stations are just too close together to justify 2 new underground stations and the interchange benefits of serving Central would be significantly better than those at Queen Street.
