@GARL_2_0 A third was put in place for the GARL between Glasgow central and Paisley Gilmour street, it was suggested for two additional tracks but the Scottish government felt one would be fine. I would suggest building the original GARL and Glasgow Cross which is already there.
@AviationNews_UK why not the original GARL and include Glasgow Crossrail in it this allows trains from Edinburgh via Falkirk and Bathgate offering a direct services to the airport , and the north. Why waste money when the link can be built from St James station which is just over a mile .