PB role: design for target cost estimate, tender design for design and construction bid, detailed design (Stage 1); tender and detailed design of bridges and retaining structures (Stage 2)

The Central Motorway Junction (CMJ) in Auckland, New Zealand, is where the Southern, Northwestern and Northern Motorways converge, just west of the city centre. Known as ‘Spaghetti Junction’, the area is a geometrically complex system of motorways and connecting ramps at multiple levels, carrying around 200,000 vehicles per day within a very restricted area.

Built in the 1970s, the CMJ has now been successfully upgraded. Stage 1 of the upgrade was completed in December 2004, and Stage 2 in late 2006.

Elevated viaduct structures and retaining walls formed a major component of the upgrade, with detailed design of these structures undertaken by PB. Major challenges for design of the structural works were the physical constraints of the area, construction staging requirements allowing for the motorway to keep operating during construction, complexities in upgrade of existing structures, and design for a seismically active area.

Bridge structures included four new viaducts, the longest of which was 253 m. In addition, the existing Newton No.1 viaduct and Wellington Street Bridge were assessed to determine their condition and capacity for seismic and gravity loads, and provided with upgraded traffic barriers.

PB’s work on the CMJ upgrades is an excellent example of effectively balancing competing demands in an urban transport infrastructure environment. The bridge structures are the result of complex geometry constraints within an intricate motorway system. The project’s success required creative geometrical solutions made possible by innovative and efficient bridge designs.

2005: Winner, Infrastructure Award, New Zealand Concrete Society