More spaghetti to help untangle Auckland junction

The temporary southbound lanes (R) enable work to progress on new lanes and the southern terminal (C). Picture / Richard Robinson. Click on 'more pictures' below for a graphic showing the changes.

Fresh lanes to provide two new major routes through Auckland's Central Motorway Junction are snaking over a section of the Southern Motorway.

The work in the Spaghetti Junction is so complicated and tight that engineers liken designing the new roads to putting a thread through six needles at once.

The new lanes will provide direct routes from the Auckland Harbour Bridge to the Northwestern Motorway. And from the harbour bridge to the Port of Auckland through Grafton Gully.

The present work by the Wellington St overbridge also involves two new Southern Motorway southbound lanes (SH1) which look like they are heading into a tunnel.

The work requires lowering these lanes by up to 3.5m to allow the two northwestern and port lanes to bridge over the top, approximately 6.5m above the lowered SH1.

After this short dip the southbound motorway lanes will climb again to where the motorway meets the Hobson St on-ramps.

The new southern "tunnel" lanes are a replacement for the present southbound lanes used by motorists as they come up from the Victoria Park Viaduct, under the Wellington St overbridge and into Spaghetti Junction, which is used by over 200,000 vehicles a day.

The present SH1 southbound lanes are in fact disposable "sacrifice" lanes built to get southbound traffic through the area while a raft of permanent links are built.

The overall plan under the Central Motorway Junction $140m Stage 2 scheme - due to be finished about the end of the year - involves fitting many elements into the existing corridor of land designated for motorways.

In places the foundations of existing structures are being shaved off and given design and shape changes just to make everything fit.

The space available for the motorway in the Wellington St area has been widened as far as possible by using big new vertical retaining walls in place of the previous embankments.

The Northern and Southern motorways meet at the Wellington St Bridge. Not far north of there, near the Cook St off-ramp, the new lanes to the port and Northwestern can now be seen leaving the southbound lane on the left-hand side, then climbing above and crossing it.

The curving nature of these two new lanes has allowed engineers to use supporting beams alongside with gaps between, allowing more light to reach the length of lowered Southern Motorway lanes within the tunnel below.

Full funding has been allocated to the $195 million Spaghetti Junction project, which is due to be finished by the end of the year.

Construction of some new routes, like the Northwestern to Northern and the Port to Northern, will be substantially completed before that.

However, they cannot be used until the other works in the congested construction site around Wellington St are complete.

Work, such as the extra lane on the Northwestern (SH16) from Newton Rd to Western Springs and from Bond Street to Newton Rd in the direction of the city will also be completed and opened to traffic by Christmas.

When the whole junction is finished, a $20 million system of traffic management signs (similar to the current lane control signals on the Harbour Bridge) and on-ramp traffic flow control signals will have been installed.

This work, including 20 new gantries across the many lanes, will be done mostly late at night and should be finished by next May.