Drivers heading to central Auckland from the Northwestern Motorway must this morning overcome many years of conditioning, and look for an offramp to their left, rather than right.

Almost 20 years of jostling to reach the motorway's two right-hand lanes to get to Auckland City or North Shore ended yesterday with the closure of the old Nelson St offramp.

From this morning, motorists will use a left-hand offramp which splits from the motorway just after the Newton Rd exit.

The change will affect all motorists heading north, south or east, and not just those turning off at Nelson St, as traffic headed for the Southern Motorway or the port will have to get used to being in right-hand lanes.

Transit New Zealand is acutely aware of the confusion this may cause, and had agents blitzing vehicles on offramps last week with leaflets to explain the changes.

A bus driver noticing final work on Friday on the new Nelson St offramp said he would not want to be anywhere near it this morning because of the difficulty he feared for motorists trying to get to the left past queues of traffic wanting to go south.

"It could be a complete shambles."

An average 8000 vehicles head south or to the port from the Northwestern Motorway in the three-hour morning peak from 6am to 9am, and 4000 use the Nelson St exit.

But Transit regional manager Richard Hancy said the new lane configurations would ultimately improve safety in bringing motorway exits more in line with the "keep left" principle.

He said all motorists would need to read large overhead signs, both permanent and on variable electronic message displays, to direct them to the correct lane.

Signs starting almost 1km west of the new layout will tell motorists heading for the Newton Rd offramp to choose the extreme left approach lane and those looking for Nelson St need to be in the next lane over.

Traffic bound for the Southern Motorway need to be in the third lane from the left, and those for the port and East Auckland should be to the extreme right.

Northbound traffic will have to keep dog-legging past Nelson St to Union St and the Wellington St bridge for now to get to the Northern Motorway.

But Mr Hancy said they would have their own direct motorway-to-motorway link by the end of next year, when another ramp opened.

A new left-hand offramp to Nelson St is also being built from SH1.

* Motorists will also have to be extra wary along Albert St in central Auckland in today's morning traffic, with the arrival of hundreds of North Shore buses, many of which previously ran along Hobson St.

The Auckland City Council has had new bus lanes operating along large parts of Albert St, mainly southbound, for the past week to help motorists get used to avoiding them before the buses arrived.