Ministers were understood to be concerned over SPT's ability to deliver such a major scheme on time and to budget, especially as its delivery of the much smaller £12M Partick Interchange scheme had suffered delays.
Announcing the change last Friday, Scottish transport minister Stewart Stevenson said: "As with all infrastructure projects funded from the public purse, the objective must always be to deliver as effectively and as efficiently as possible. This represents the right way forward for GARL."
The scheme is due on site in 2009 with operations beginning in 2012, well before the July 2014 Games. It includes upgrading of the 9km of route between Paisley Gilmour Street and Glasgow Central as well as the new railway.