 At this time the line that became the Liverpool Overhead Railway was being designed.The solution of building an urban railway over the streets in the central area seemed attractive and relatively cheap, and on that basis the Glasgow Central Railway obtained Parliamentary authorisation on 10 August 1888.

Business interests and public opinion in Glasgow only now realised what was being proposed, and a considerable outcry; so vehement was it that the Caledonian reconsidered, and a further Act was sought and obtained the following year, altering the plan to a sub-surface line like the NBR line.Getting the Act was one thing, but the detailed engineering of a sub-surface railway through the centre of the city, with large buildings that could not be disturbed, was daunting.