Grafton Bridge - designed a century ago for horses and early cars - will receive space-age joint replacements as the centrepiece of a $21 million rapid transit corridor to Newmarket.
Work on the corridor is expected to start in April, and the bridge is likely to be closed for up to two months during strengthening operations before the project is complete towards the end of 2007.
The immediate goal is to give buses a clear run along dedicated lanes much of the way between Britomart and Newmarket - up Symonds St, across the bridge and past Auckland City Hospital in Park Rd before joining the lower end of Khyber Pass Rd.
Landscaping and tree-planting is aimed at encouraging walking and cycling, and new shelters will be built at main bus stops.
But the bridge, the world's largest single-span concrete structure when it opened in 1910 to replace a foot crossing of Grafton Gully, is being made strong enough to carry a possible light-rail system in a new lease of life which engineers say should last 100 years.
It will remain closed to day-time general traffic once the corridor is open, leaving it as a dedicated busway between 7am and 7pm, to be shared by just bicycles, pedestrians and emergency vehicles.
Cars will be allowed across only at night, as will trucks, which are now banned because of a 14-tonne weight limit.
New anchors under two main piers spanning the motorway to the waterfront, and carbon-fibre stronger than steel beneath its beams, will make it earthquake-resistant and allow it to carry vehicles of up to 40 tonnes.
Despite the existing weight limit, Auckland City Mayor Dick Hubbard marvelled yesterday at the achievement of the bridge-builders.
"All credit to the engineers who built something designed to take Model T Fords and horses and carts, and now modern buses and light rail," he said, while inspecting the foundations.
"I just wish the same degree of foresight could have been shown by those who built more recent structures like the Aotea [Civic] car park."
Auckland City Council project manager Graham Long said that although the strengthening could take up to a year at a cost of $3 million to $4 million, most of the work was below the surface and he hoped the bridge would be closed to traffic for no more than two months.
Hospital authorities have asked for two months' notice to alert patients and ensure emergency vehicles can plan alternative routes.
A particular challenge will be to avoid disturbing 19th-century graves over which the bridge was built in the Symonds St Cemetery, final resting place of Governor William Hobson.
The council expects the transit corridor to cut up to 14 minutes off peak-hour bus trips between Auckland and Newmarket, which Stagecoach acknowledges can take half an hour in heavy traffic.
Up to 29,000 bus passengers are expected through the corridor daily.
Although all but about $900,000 of the cost will be covered by Government and regional grants, Mr Hubbard said the project was a major undertaking for the council, providing a vital link between the city's two main retail and commercial hubs.
It would also be an extension to the Northern Busway, allowing commuters from over the harbour bridge easy trips to Newmarket and points further south via Britomart.
Asked why a rapid transit road route was needed when trains took just eight minutes to reach Newmarket from Britomart, he noted that buses passed the city's two largest employment centres, Auckland University and the hospital.
Although about 13,000 cars will be diverted from Grafton Bridge each day, residents remain unhappy that these will be replaced by up to 1500 buses.
Consultants say reduced delays to buses now often stuck in traffic in Khyber Pass Rd will cut pollution over a general area including the bridge by 10 per cent to 20 per cent, but acknowledge that diesel particulate emissions in Park Rd could rise by 120 per cent.
But they predict engine improvements will shrink that figure back to a 20 per cent net increase by 2011.
Detailed designs for the Central Transit Corridor will be on display for public comment from today until November 30 at Auckland City Hospital, and from December 1 to 9 at Britomart. They can also be viewed at www.aucklandcity.govt.nz/ctc (see link below).