The story of road engineering in a country such as New Zealand would be incomplete without reference to the bridge engineers. Recent advances in this field have been quite as outstanding as in those of roadway design. Like many of the early roads, some of the first bridges built in the colony are still open to traffic or have just been replaced, as, for example, the Kawarau Bridge (1962) on the Cromwell-Queenstown route. The old bridge (1880) was a suspension one with a 300-ft span. The Wanganui Bridge, which originally had lift spans, was erected in 1869 and still serves the city. Bridges of standardised design in steel and pre-stressed concrete speed up construction by pre-fabrication methods, and decrease the work to be done on the site. Again, new concepts and construction techniques, such as the use of steel piling in various forms, prestressed concrete piles, or bored piles, have enabled structures to be built where timber or ordinary concrete piles would have been inadequate. Construction by cantilevering out from piers has been recently used on a number of major bridges in New Zealand. This is a procedure which can be used on difficult sites.
As in road engineering, bridge design must be related to traffic requirements. In the early days the approaches to a bridge were of minor importance and every effort was made to secure the shortest and cheapest site. Moreover, bridges were designed for smaller loads than those required by modern traffic. Today a bridge is considered part of a highway and must be constructed in conformity with the curves and alignment of the road. But bridge construction is also designed for other purposes, equally important. The extension of overhead motorways into the heart of Wellington and of Auckland will require many major structures over land and rail.