KEY POINTS:
A seamless motorway-to-motorway connection at the southern entrance to Auckland's western ring route is sprouting up in the form of a 240 metre flyover leading to several new bridges through Manukau City.
As the two-lane flyover takes shape above the Southern Motorway - for traffic heading to SH20 and the airport from the north - excavation work is starting below it on a "cut-and-cover" tunnel for southbound vehicles travelling from the west.
That should allow traffic to flow in two new directions through a triple-level interchange at the eastern end of the 4.5km Manukau motorway extension, which Australian-New Zealand joint venture Leighton Works is building for Transit NZ for $210 million. It is expected to be finished by 2010.
Work is well-advanced on six of the project's 12 bridges needed to carry the new road in a swathe from central Manukau to the existing Puhinui interchange at the southern end of the Southwestern Motorway, one of the two main routes to the airport.
Those already partly or largely completed include bridges to carry Gt South Rd, Barrowcliffe Place, Wiri Station Rd and Lambie Drive over the new motorway, which will have two traffic lanes in each direction and room for future widening.
Construction of a bridge to take Plunket Ave over the motorway has yet to start, but embankments are being built further west to carry the road over the main-trunk railway line and over a $14 million extension by Manukau City Council of a widened Cavendish Drive from what are now Liverpool and Nesdale Streets.
There will also be two bridges over the Puhinui Stream, which has been diverted to run through big culverts.
Initial traffic management has included diverting vehicles to temporary alignments along Gt South Rd and Lambie Drive, and moving an entire section of the Southern Motorway westward to allow piles to be driven into the ground for the tunnel beneath it.
Once the lid of the tunnel is in place, that motorway will return to its old alignment in two stages to allow the remaining piers of the 13-span flyover to be erected.
The next milestone of the project is likely to be at the end of this month, with the closure of a section of Roscommon Rd in Wiri to traffic. Drivers will have to use the Puhinui Rd interchange as a detour until then.
A section of Davies Ave near the Manukau City centre also faces temporary closure from about June, to allow a minor realignment of Wiri Station Rd.
