Wellington Urban Motorway, State Highway 1
This section of State Highway 1 in Wellington city, from Ngauranga Gorge to Willis Street, embodied innovative techniques in design and construction to give an environmentally sensitive development. The length between the Thorndon overbridge and Willis Street was opened to traffic in 1978. Construction took a total of 18 years and consisted of several contracts.
The urban motorway contains 15 bridge structures and one tunnel. The tight constraints on geometric layout resulting from the varying topography, the proximity of the hillside and the narrowness of available corridors, were all overcome in a short length of motorway, which makes this project unique.
The Thorndon overbridge's foundation work began in 1965 with the reinforced and prestressed concrete bridge eventually opened in 1968. Bolton Street and Aurora Terrace bridges were the first in the world to be protected from earthquake forces by the use of lead extrusion dampers. The Ngauranga bridges were the first incrementally launched prestressed concrete box-girder bridges in Australasia.
The Terrace Tunnel is thought to be the largest cross-section road tunnel in New Zealand, being 12.8 metres (m) wide from wall to wall and 7.9 m high. More than 2,000 tonnes of structural steel arches were needed to support the section of city that lay on top of it because the tunnel passed through the bad ground of the major Wellington fault.
The Wellington Motorway forms a boundary between the residential and commercial sections of the northern end of the city, and lies at the foot of steep hillsides on part of which is prime housing. The project was particularly significant in that it required the intrusion of a motorway system within the already built-up section of inner Wellington. A large effort was made to make sure the system blended with the environment. Because of the varying topography and its constraints, about one third of motorway is carried on bridge structure. The Terrace Tunnel design endeavoured to keep disruption to the existing steep surrounding land form to a minimum, as this land contains not only housing but also bush. Consequently, retaining walls up to 15 m high were designed for the approaches to the tunnel portals.
The motorway forms an important part of the State Highway system. It was built in a geologically complex terrain to cope with high traffic volumes in an already built-up section of inner Wellington. The effort expended in making sure the system blended with the environment was rewarded by the conferring of the Institution of Professional Engineers New Zealand (IPENZ) Environmental Award in 1972.
IPENZ “Engineering to 1990” project
This item of New Zealand’s engineering heritage was recognised as part of the IPENZ “Engineering to 1990” project, which the Institution organised to help celebrate the country’s sesquicentenary in 1990. A plaque was unveiled to mark the significance of this motorway system as part of the development of the nation.
State Highway 1 between Ngauranga Gorge and Willis Street, Wellington.
The IPENZ 1990 plaque is in Hill Street adjacent to the overbridge.
This section of State Highway 1 is available for public vehicle use at all times.
Additional image gallery details
Motorway under construction at Shell Gully, Wellington . Negatives of the Evening Post newspaper. Ref: 1/4-028066-F. Alexander Turnbull Library, Wellington, New Zealand.
Wellington Urban Motorway under construction at Shell Gully [circa 7 August 1974]. Evening post (Newspaper. 1865-2002): Photographic negatives and prints of the Evening Post newspaper. Ref: PAColl-9150-24. Alexander Turnbull Library, Wellington, New Zealand.
Permission of the Alexander Turnbull Library, Wellington, New Zealand, must be obtained before any re-use of these images.