The New Zealand Railways Magazine, Volume 4, Issue 5 (September 1, 1929)
In a statement to the Press the Hon. W.B Taverner (Minister of Railways) gives some interesting particulars regarding the rebuilding programme of the Department in the matter of bridges.
The Government's policy of giving New Zealand industries as much support as possible in contracts for public works is exemplified in the recent acceptance of tenders for the new Ngaruawahia and Whenuakura bridges. The steel plates and shapes (a total weight of 500 tons) will be imported from Great Britain, but the whole of the fabrication of the steel work will be done in the Dominion.
In addition of the encouragement of local industry, these works have another interesting aspect as they mark the beginning of an extensive programme of reconstruction of the old original timber bridges.
Altogether, the New Zealand railway system has about 53 miles of bridges, including a total length of about 32 miles of timber construction. Most of the old wooden bridges were made of native timber, chiefly kauri or totara. They served their purpose well under the lighter traffic of the past, but they have to be replaced now by stronger structures to meet the new needs of the much-changed times. Increasing traffic has demanded the adoption of heavier types of engines, exceeding the weights for which the bridges were originally designed, and native timbers in bridges have been wholly replaced with the stronger and more durable Australian hardwoods. These, in turn, have a limited life, and as the need for heavier engines still persists, and timber increases in cost, it becomes uneconomical to maintain the original types of bridges in service. Therefore reconstruction in steel and concrete to a high standard of strength is found advisable.
Attention is being focused first of all upon important main lines, so that restrictions on the running of some of the heavier engines can be removed, with the resulting economies in traffic operation.