That 'Bridge to Nowhere' is finally going somewhere

Work is being done in the dead of night to avoid traffic disruption. Picture / Greg Bowker

For months they have been calling it the Bridge to Nowhere, jutting out from a high level at Spaghetti Junction, in the centre of Auckland's motorway network.

Now it is beginning to be a bridge to somewhere.

It is in fact part of the vital link between the Port of Auckland and the Northern Motorway. It will snake through the numerous other links - north, south and northwest - also being installed in the area.

The bridge now being constructed comes out from under the Karangahape Rd bridge.

One end of the bridge structure connects onto the end of the old Ramp B, a massive concrete structure erected for a Dominion Rd link years ago but never used.

A new separate structure on top of the old ramp carries the new link across it.

Progress on the new link awaits one more vital support pier which has to be built in the present Hobson to Northwestern Motorway carriageway.

That means swapping that traffic onto another carriageway.

Swapping traffic around in Spaghetti Junction to keep the motorways operating while the many new links are being built is a complex challenge.

An engineer this week likened it to doing one of those puzzles made of moveable squares with only one vacant space in which to make the next move.

One of the keys in the present puzzle will be the opening of the new Northwestern to Nelson off-ramp which city-bound motorists will reach by way of a safer left-hand exit, instead of the present one to the right. That is expected to happen around the end of this month.

The beams for the new port to northern route are some of the 92 needed for the present $140 million Central Motorway Junction Stage 2 project. They are being installed on four bridge/viaduct structures in the area.

The work has to be done in the dead of night, when motorway traffic can be diverted.

The beams involve considerable engineering design, manufacture and installation skills.

As long as 39m each and as heavy as 58 tonnes, they are being cast at a special site in Mangere, for reasons of economy, speed and quality control.

Because of the twists and turns in the motorway junction lanes the beams are made in a special mould which can be adjusted to cater for different curves and cambers in the structures being built. Their design includes stressed reinforcing in their bases which helps save weight.

Even so, getting them in place involves one of the heaviest trucking units in New Zealand, essentially a front and a rear vehicle with the beam becoming part of the vehicle during the trip from Mangere to the Central Motorway Junction.

It takes about 90 minutes (at about 20km/h) even at night with light traffic.

The weight is such that the drivers are instructed to stay in particular parts of roads or bridges during the journey to avoid structural damage. In the central city two cranes with a maximum lift capacity of 200 tonnes each lift the beams across to the piers.

On top of the beams between the piers goes the new road structure, including reinforced concrete, the road surface, safety barriers and all the other features of a modern motorway.

The Port to Northern link should open in November 2006.Key link

* Yet another major link - Port to Northern Motorway - is advancing through Spaghetti Junction.

* It should be completed by the end of next year.

* Special pre-cast beams being used in this and other new structures weigh up to 58 tonnes each.