In rail terms, Glasgow is a giant. Its population...[are] kept moving by the UK’s best suburban rail network outside of London... But ...Glasgow’s rail network faces serious problems.
Most of the lines emanate from Glasgow Central station and face southwards... A smaller number of lines face northwards out of Glasgow Queen Street station .... There is, notably, no direct rail connection between Central and Queen Street. The capacity of this station and the lines approaching it have been reached. Trains are already overcrowded, and this is only going to get worse. It’s beginning to impact the timetable, making services less reliable.
Everything depends on solving the Glasgow Central problem. To do that, we’d need a tunnel. This would allow south-facing services that currently pile up inside Central station to run through the new station to Queen Street and onwards onto lines facing northwards. While terminus stations like Central are limited by the time needed to turn trains around, a through-running station can provide capacity for as many as 24tph on just two platforms.