$142m plan to rebuild viaduct

One of the most congested parts of the Auckland motorway system, the Newmarket Viaduct, will be replaced at a cost of $142 million but with minimal disruption to traffic.

The new structure will have an extra lane to ease congestion on the Southern Motorway, which now carries about 200,000 vehicles a day - the highest volume of traffic in the country.

The new viaduct will look similar to the present 700m long and 28m high one opened in 1966. But it will have higher earthquake-resistance and safety standards.

Higher, stronger barriers are being designed to prevent trucks plunging off the viaduct in accidents.

Transit NZ's regional manager in Auckland, Richard Hancy, said yesterday that construction was expected to start in 2008-09.

Building should take two or three years.

Asked about possible tolling, Mr Hancy said: "We have no plans to toll the Newmarket Viaduct."

The finished structure will include four southbound lanes and three northbound, instead of the present six lanes.

It is an essential complement to the present extensive motorway construction aimed at easing congestion in Spaghetti Junction.

An additional lane - which alone will cost $31 million - on the left-hand side of the existing three southbound motorway lanes will allow a substantial amount of traffic to get off the motorway at Greenlane using two lanes.

The rest will flow south on the other two lanes.

One side of the new viaduct will be 13m east - towards the sea - of the present structure.

This is part of a deceptively simple scheme for replacing the present viaduct while still providing six lanes at all daytime and rush-hour times along the vital Southern Motorway route.

Construction will start with four new lanes on the eastern side of the viaduct, followed by the demolition of the present southbound lanes.

These will then be replaced by the rest of the new structure, allowing the old northbound lanes to be demolished.

The new plan follows a lengthy examination of alternatives including revamping part of the existing viaduct, at an estimated cost of $85 million.

Mr Hancy said a number of features of the existing viaduct do not meet modern design standards, including its median and edge barriers, traffic-load capacity and lane and shoulder widths.

The present structure is also designed to withstand a one in 500 years magnitude earthquake.

Modern standards insist on 2500 to 5000 years.

Because the new viaduct will be partly to the side of the present one, Transit NZ will have to buy some land for where the bridge piers go into the ground.

* Transit NZ will hold an open day for the Newmarket Viaduct improvement project from 10am to 4pm on Saturday, October 8, at the Officers' Club, 14 Edgerley Ave, Newmarket.