Mega-trucks too heavy for motorway

Only three permits have been issued for Auckland. Photo / Paul Estcourt

Auckland's Southern Motorway - one of New Zealand's busiest highways - has up to a dozen points too weak to support new, extra-heavy trucks already plying the roads.

The Transport Agency admits it will take years of strengthening to make the collection of bridges and other structures "compliant" for the new trucks, weighing up to 53 tonnes, and up to 22m long.

Auckland Harbour Bridge has also yet to be cleared for use by the new big trucks, though a structural feasibility study is under way.

The agency has received 366 applications to use the new trucks on public roads under a permit scheme introduced in May for "high productivity motor vehicles".

It has so far issued 58 permits, mainly for those covering routes in the South Island and the lower half of the North Island.

Only three permits have been issued for Auckland, all for arterial roads away from the motorway, between Otahuhu and Penrose.

A further 62 applications have been declined and 246 are still being assessed.

Spokesman Andy Knackstedt said most declined applications failed because of inaccurate information or not meeting legal requirements such as maximum axle loadings.

The agency has issued a list of 11 structures on the Southern Motorway and two on its long Grafton Gully on-ramp needing structural assessments of whether they need strengthening for use by the new trucks.

These include bridges over Tamaki River and Puhinui Stream.

The southbound Takanini motorway off-ramp bridge over Spartan Rd had been assessed and was likely to be strengthened in the next year, Mr Knackstedt said.

Assessments of the other structures were due to be completed by the end of this year.

Agency regional state highways manager Tommy Parker said the organisation was committed to preparing the Auckland-to-Hamilton route for heavier and longer loads, and was working on a programme to upgrade the Southern Motorway's weak links.

"Some are fairly small jobs, perhaps just needing strengthened embankments," he said.

The agency hoped to complete the programme "over a few years".

Mr Parker said the $215 million replacement Newmarket Viaduct would be able to carry heavier loads, although the existing structure would not be up to scratch.

But he said the agency would be keen to encourage trucks in the new vehicle classes to use Auckland's western ring route rather than the harbour bridge and Spaghetti Junction.

He acknowledged it would be some time before heavier or longer trucks would be able to use the Southern Motorway to carry goods to or from Auckland's port, though there was potential for consignments to be split up and sent on shuttle trains between the port company's new inland distribution centre at Wiri and the waterfront.

High-productivity permits:

Issued to individual truck and trailer units for regular trips on specific routes.

* Length allowed - 22m (standard maximum length - 20m).

* Weight allowed - 53 tonnes (standard maximum weight - 44 tonnes).