A few more details on central Scotland railway improvements here:
http://news.scotsman.com/edinburgh/Airport39s-tramtrain-hub-will-go.6785793.jp
"[...] some trains on the main Edinburgh-Glasgow line, which will be diverted via Gogar from their current route to the south of the airport.
Network Rail said this re-routing, taking trains on a new loop via Dalmeny, near South Queensferry, would also be required whatever the fate of the tram scheme, to free up space on the existing line."
And also...
"Other routes to be speeded up thanks to electrification include lines between Edinburgh and Glasgow and Dunblane and Alloa. More frequent services will also operate on a secondary Edinburgh-Glasgow route via Carstairs."
Good that the Dunblane line might be in the queue for improvements.
Of course, the main thrust of The Scotsman article is:
"A NEW tram-train interchange will be built to serve Edinburgh Airport as part of Scotland's biggest rail upgrade even if the tram scheme is shelved, The Scotsman has learned."