KEY POINTS:
Major strengthening work on the Auckland Harbour Bridge is being fast-tracked to protect the transport lifeline from punishing fatigue stress caused by heavy traffic.
Transit NZ confirmed last night that it intends restructuring its 10-year state highway forecast to make $45 million available to complete work on the bridge's clip-on structures in about 2 1/2 years, from as early as December.
That is just half the five years the highways agency earlier expected to take for the job, which follows a detailed engineering review it began in 2004 of the bridge's ability to carry growing traffic loads for at least another 20 years.
Although Transit has banned trucks weighing 13 tonnes or more from the outer clip-on lane on each side of the bridge since July, to reduce fatigue stress, chief executive Rick van Barneveld strongly denies that the structures are in worse repair than earlier thought.
"The idea that metal fatigue is more advanced than had been thought is not the case," he assured the Herald.
But he said Transit regarded it as good practice, now that consultants had identified a need to strengthen the clip-ons to cope with increased traffic loads, to complete the task earlier than originally intended.
"There is no difference to a pothole which develops in a road, and then you make a decision [to] let's get on and have a systematic way of treating it," Mr van Barneveld said.
"It is critical to stress that the bridge is safe and the upgrade is planned preventive maintenance work similar to that carried out a number of times since the clip-ons were opened in 1969.
"The 165,000-vehicle-per-day lifeline that is the Auckland Harbour Bridge is going to be around forever and will continue to provide service to Auckland and the rest of the country."
Mr van Barneveld said additions of extra steel made to the clip-ons over the years meant they were stronger than when they opened.
The plan now was to strengthen a range of components in the hollow box girders directly under the traffic lanes, including adding extra steel to their cross-beams.
A secondary task would be to stiffen and strengthen the attachments of large steel angle brackets under the clip-ons to five of the seven concrete piers supporting the bridge across the Waitemata Harbour.
The steel extensions would enable the bridge to meet extra traffic demand expected to be generated on both sides of the harbour by the 2011 Rugby World Cup.
Any diversions of traffic to the central bridge would, if needed, be temporary and made at night to limit disruption.
Mr van Barneveld said he was satisfied that the existing ban on heavy traffic on the outer clip-on lanes, which had eased load pressures on them by 20 per cent, was adequate without having to introduce more restrictions.
He had been assured by the Beca consultancy, which had had its engineering study of the bridge upheld by an international peer review, that there was no need to ban heavy traffic from the inner clip-on lanes as well.
Auckland City Mayor Dick Hubbard said he accepted an assurance offered to him by Mr van Barneveld last night that the clip-ons would remain safe to drive across, despite the need for the extra steel to stop them flexing with age.
"I have confidence in driving over them that there is no chance they are going to fall off."
But he said the need for such extensive maintenance highlighted a need to plan for an extra harbour crossing to reduce Auckland's dependence on "that single ribbon of steel".
Transit is working with the Auckland Regional Council and the Auckland and North Shore cities to pick the best route for the new crossing, which it believes should be a tunnel costing about $3 billion.
