The agency has also confirmed that as well as closing Newmarket Viaduct's northbound carriageway for up to 39 hours, it will block four entry points to the Southern Motorway to northbound traffic. These reach as far away as the Southeastern Motorway northbound on-ramp, which is 6km from the viaduct.
The Southern Motorway is being closed while workers prepare to divert northbound lanes on to the new 690m section of the viaduct and shift the blue 800-tonne lifting gantry used in the viaduct's construction.
Acting state highways manager for Auckland and North Steve Mutton said detours would be set up that would divert on to local roads the 65,000 cars that normally use the closed section of motorway on a Sunday.
Off-ramps would be closed in order to keep detoured traffic moving.
Mr Mutton said motorists could expect particularly heavy traffic in the following areas:
* Newmarket (Gillies Ave, Broadway, Alpers Ave, Great South Rd, Khyber Pass Rd and Remuera Rd).
* Greenlane (Green Lane West, Green Lane East and Gt South Rd).
* Remuera (Orakei Rd, Ascot Ave and Market Rd).
When the viaduct's northbound lanes closed at 5pm tomorrow, local roads would have to cope with an extra 4000 vehicles an hour and by noon on Sunday the volume would reach 4600.
The agency has put up signs as far south as Manukau to remind people to use the Southwestern Motorway in order to skirt round the clogged Newmarket and Greenlane areas if they are heading to West Auckland or north of Silverdale.
Mr Mutton said regional highways would also be busy as it was the Auckland Anniversary weekend.
He suggested people could have smoother and more reliable trip times by travelling outside peak times.
By 8am Monday, the new viaduct lanes would be open - before traffic built up in the race to the waterfront for prime viewing and picnic spots for the Auckland Anniversary Day Regatta.
However, roading managers are aware that the closure on Sunday coincides with the Auckland Seafood Festival, which draws up to 22,000 people to the Wynyard Quarter in downtown Auckland.
Mr Mutton recalled that in September 2010 the southbound lanes of the viaduct were closed for the same reason for 17 hours.
On that occasion, Aucklanders heeded the warning and steered clear of Newmarket.
Traffic on major arterial routes was half normal levels.
This time, the northern side has a greater choice of off-ramps to get traffic on to detour routes.
In 2010, the use of trains was credited with cutting down traffic.
Auckland Transport spokeswoman Sharon Hunter said yesterday that in the critical Newmarket area more trains would be running.
Usual weekend work to prepare for the introduction of electric trains would be deferred in order to keep the Southern Line open north of Otahuhu.
However, buses would replace trains during the weekend to carry out essential works on the Eastern Line - Papakura to Britomart via Glen Innes and on the Southern Line between Papakura and Otahuhu.
People coming from Papakura to the city would be on a RailBus from Papakura to Otahuhu then change to a train at Otahuhu Station.
This would apply tomorrow, Sunday and Monday.
Between 10am and 6pm each day trains would run every 30 minutes.
ON THE WEB
Detour information: www.nzta.govt.nz/aklsummerseason or facebook.com/switchmyroute
State highway information: www.highwayinfo.govt.nz
