KEY POINTS:
One of North Shore City's main motorway connections closes tonight for the weekend, before a new link opens early on Monday in conjunction with an extension of the $295 million Northern Busway.
The Transport Agency intends closing the southbound motorway onramp to the harbour bridge from Onewa Rd
- a key link for residents of suburbs such as Birkenhead and Northcote - at 10pm.
That is to allow a new onramp to be connected over the weekend to the interchange, which is being reconfigured as a key part of the $40 million final stage of the busway between Constellation Drive and the harbour bridge.
The ramp forms one of two new bridges over the motorway, between Onewa Rd and Waitemata Harbour.
Another bridge, to restore motorway traffic movements to Onewa Rd from the north after almost a year and a half of detours, is expected to open late next month or in November.
The two bridges will replace a single structure which for many years carried opposing traffic along one lane in each direction, over tight curves and with no separation barrier to prevent head-on smashes.
Transport Agency acting regional manager Tommy Parker said the old structure had to be demolished before the offramp could be completed, and a new northbound bus priority lane built along the motorway.
Moving traffic from the old structure to the new onramp would allow demolition to start.
The busway will meanwhile be extended south by 890m on Monday morning, to skirt around the seaward side of the motorway interchange, to the foot of the harbour bridge.
At that stage, the busway will be 8.74km long, comprising a two-way dedicated bus highway for 6.24km from Constellation Drive to Esmonde Rd, then a 2.5km single-lane southbound-only stretch past the Onewa interchange.
Buses from Onewa Rd will be able to join the busway from a priority lane on the new onramp, while general traffic will use a right-hand lane to reach the motorway.
Mr Parker said the busway extension would allow buses to get past bottlenecks near the Onewa interchange, before joining the motorway on the relatively free-flowing approach to the harbour bridge.
About 38,000 vehicles pass through the Onewa interchange each day, a figure expected to rise by 5000 or so once the motorway offramp opens from the north.
Although trees and shrubs have been planted in the middle of the interchange, a coastal slope between the new onramp and the busway has been left barren with the exception of rudimentary platforms to encourage protected dotterells to roost.