It appears that the NZ Transport Agency is trying to avoid constructing an underpass by pricing it into oblivion.
May I remind the NZTA of a very common and simple process called pipejacking. This is whereby suitably sized and shaped box culvert sections, with a removable cutting edge on the front, are progressively pushed section by section by hydraulic rams through the earth.
As it moves forward the spoil is progressively and safely removed from the inside. The culvert is made of segments which are of reinforced concrete, much the same as you see elsewhere in our road system. Because