Aucklanders are being urged to avoid driving during Auckland Anniversary weekend when a chunk of the country's busiest motorway will be closed for work.
Those who are planning to brave the roads have been warned to expect long delays.
From 5pm on Saturday, all of the northbound lanes on State Highway 1 between the Market Rd off-ramp and the Gillies Ave on-ramps will be closed to complete work before opening on the new northbound Newmarket Viaduct.
The Transport Agency's acting State Highways manager for Auckland and Northland, Steve Mutton, said delays would be inevitable, considerable and widespread.
"We're talking about trying to re-direct up to 65,000 vehicles on the Sunday alone," he said.
"Even with detours, the impact of the closure will be felt well beyond the Southern Motorway. If people absolutely must travel we're urging that they allow a lot more time for their journey.
"We accept that this may cause frustration - particularly on a long weekend - but our best advice is to stay away from the motorway during Auckland Anniversary weekend."
The Transport Agency has taken advantage of the three-day weekend to switch the motorway's northbound lanes across to the new viaduct.
At the same time, the blue lifting gantry used for the viaduct's construction has to be moved on to the existing northbound viaduct to help with its demolition.
Detours will be in place and detour routes to key destinations are available online.
But Mr Mutton said Aucklanders should avoid driving if possible because those alternative routes would not be able to cope if regular weekend traffic flows occurred.
"Even with a managed closure and detours in place, congestion will be extensive."
He said the Transport Agency would appreciate support and patience from motorists and that they would be working hard to finish as quickly as possible.
"We've had fantastic support from drivers while we've replaced the old viaduct and we're now asking people to help us again to keep the city moving through this closure."
The Automobile Association spokesman Simon Lambourne also urged people to avoid unnecessary trips and said motorists should plan their journeys and drive with patience and care.
"Congestion will be significant with the closure of the northbound lanes ... but the short-term pain will be well worth it given the long-term benefits of the new viaduct."
In September 2010, the motorway's southbound lanes were closed for 36 hours to complete similar work toward the $215 million project to replace the viaduct.
Aucklanders heeded the NZTA's advice to avoid the roads and the work was completed 17 hours before deadline.
Mr Mutton said the project was significantly ahead of schedule which was a "remarkable achievement".
Like the old viaduct built in 1965, its replacement is almost 700m long but it has wider lanes, is seismically stronger and will produce less traffic noise.
DATES AND DETOURS
* Northbound lanes of the Southern Motorway will be closed from 5pm Saturday, January 28 until the following Monday morning.
* Motorists are advised to avoid the motorway if possible. Either switch your mode of transport or keep your travel very local.