Mr Parker said yesterday that the agency was delighted so many people wanted to inspect the tunnel, which is the main feature of a $406 million motorway enlargement programme between Spaghetti Junction and Auckland Harbour Bridge.
"Constructing something the size of this tunnel in the middle of a city is never easy and the support we've had from the community has made a challenging job a whole lot easier," he said. "Opening up the tunnel for Saturday's walk is a small way of saying thank you to Aucklanders."
Requiring people to register was necessary for safety reasons, as the only practical way to get so many people through the tunnel was by emergency stairwells.
"These are steep, which means the numbers coming and going from the tunnel at any one time must be managed."
The tunnel was dug through the park as an open cut to an average depth of 8m, and a maximum of 13m, over which a lid was laid on 360 roof beams.
Contractors are still working around the site, including a widened motorway through St Marys Bay and a footbridge over it to Westhaven, so the tunnel's third and final lane will not open until March.
At that point, the existing two-way motorway viaduct over Victoria Park will be taken over entirely by four lanes of southbound traffic.
That means a capacity gain of three lanes through what is the last major traffic bottleneck on Auckland's central motorway network, providing an expected average saving of five minutes on trips between the bridge and Newmarket.
A consortium led by Fletcher Construction began work on the link about two years ago. The work has included moving the historic Birdcage Tavern away from the site - and then back again.
Big project
Scope
* 450m northbound motorway tunnel through Victoria Park.
* Adding a lane in each direction to the motorway between the park and the Harbour Bridge.
Cost
* $406 million.
Timetable
* 2009 until March 2012, when all three northbound tunnel lanes will be open.
