The main in situ/precast concrete structure accommodates the bus station concourse at ground-floor level, with eight storeys of car parking above. From ground to first-fl oor level, it is effectively a substantial cast-in situ transfer structure, supporting the outboard and closerspaced columns of the precast car park above. The size of the transfer structure is clearly visible within the first-floor concourse where, in accordance with architectural aspirations, the concrete structure is exposed as a feature, a theme that is repeated throughout all of the interchange structures. The decision to change from in situ to precast construction for the car park was based on the benefits to programme, quality of finish, and reduction in construction traffic that precast offered over in situ construction. The patented Hill Cannon Vertical Circulation Module (VCM) car park system was chosen for the interchange as it optimises the number of parking spaces for a given area by the efficiency of its vehicle circulation arrangement, while also providing a 'user-friendly' environment.
One of the major challenges to the contractor in the construction of the structure was the tight tolerances required for the positioning of the precast Macalloy starter bars that had to be cast into the transfer structure to a tolerance of -/+ 6mm. Tight tolerances were also a feature in the production and erection of the precast works, as perimeter elements were manufactured with cast-in channels to facilitate the fixing of the feature facade spaced glazing. Another key structure within the interchange facility is the feature aerofoil canopy, which provides a highly visible link between the tram stop and bus station. The glazed canopy is 8m high and has sweptback wings in excess of 36m in length. The wings are fabricated from steel hollow sections and laser-cut steel plate suitably profiled to resemble the typified construction of an aircraft wing. The interchange became operational on 27 November 2005 and can be considered one of the growing number of landmark buildings within Manchester city centre.