NZTA have supplied us with a copy of their assessment of heavy trucks on State Highway bridges. The objective of the report is to identify bridges on freight routes that would require strengthening for higher mass limits provide an indication of costs. The full copy (8Mb) is available here, but some key points are:
Whilst the current legal limit is a gross mass of 44 tonnes, most of the bridges on the state highway network and indeed the local road network were designed and constructed to carry lower loads. However, they continue to perform beyond expectations because of the conservative nature of some designs, material strengths that are higher than allowed for or ongoing upgrades and strengthening programmes.
306 state highway bridges would require strengthening, or detailed investigation and an estimated $85M would be required to fund the work over a period of several years.
Of these bridges, only 13 have already been included on the approved 09/12 Bridge Replacement and Upgrade Programme due to their current condition. The results have not been studied in detail to determine if any of the bridges should be replaced rather than strengthened.
In the South Island, no section of SH1 has bridges that can support 50 tonne trucks. In the North Island Pokeno – Hamilton – Tirau has strong enough bridges, as does Rotorua – Taupo. No section of SH1 from Taupo to Wellington has bridges that can support 50 tonne trucks.
It is hard to see how heavy trucks can be introduced to the state highway network without doing the necessary bridge strengthening work first. The proposed implementation date of 2010 seems overly optimistic.