"We agreed we would wait for the [30-year] Auckland Plan to be finished before we updated the notice of requirement," he told the Herald.
"What we said was, we would go with the preference expressed in the Auckland Plan, and then seek guidance from the Government about the update."
Now that the council had published the plan, with a preference for road tunnels instead of a new bridge to be built between 2021 and 2030 and "future-proofed" with room to carry trains as well, the agency was free to move ahead with route protection between Spaghetti Junction in central Auckland and Esmonde Rd in Takapuna.
It was likely to provide new information to the council late this year, including a discussion of environmental issues, with an aim of opening its application to public submissions "sometime in 2014".
Although average daily traffic volumes across the harbour bridge declined by about 5 per cent between 2007 and 2011 to about 157,000 vehicles after the establishment of the Northern Busway, they rebounded by 7 per cent last year to almost 168,000 in November.
Mr Wood believes completion of the Victoria Park motorway tunnel in March is encouraging more commuters to get back in their cars after previously using the busway to beat congestion.
Having recently spent $86 million strengthening the bridge's two clip-on structures, the agency is focused mainly on its ability to cope with increasing freight loads.
Mr Town said that with careful management, there was no reason why the 54-year-old bridge could not last for another 100 years. But he said the "critical path" for bridge loads was heavy vehicles travelling on the northbound clip-on lanes, for which forecasts indicated a new crossing would be needed by 2030.
Even so, the agency did not want to build the new crossing too early, for cost reasons.
"It's expensive, so getting the timing right is the thing," he said.
The agency in early 2011 estimated the cost of a pair of road tunnels at $5.3 billion compared with $3.9 billion for a new bridge, and the Auckland Plan cites a figure of $5.8 billion to include future provision for trains.
Mr Town acknowledged that technological advances were likely to reduce tunnelling costs, while those for a new bridge were unlikely to fall markedly.
But he said "one of the big unknowns" was what the completion in 2017 of the western ring route with its connection to the Upper Harbour Bridge at Greenhithe would do for heavy traffic movements.
"It will provide a genuine heavy traffic option - between 2017 and 2021 we will be looking really closely at travel patterns."
Mr Wood said Auckland's northern sector was due for a resurgence of development, for which a new crossing was needed urgently, regardless of the western route's appeal as a bypass for some long-distance traffic.
"I'm just amazed it has started drifting in the way it has," he said of the crossing debate. "I have a real concern - the upper part of Auckland would be paralysed if anything happened to the harbour bridge."
Austerity' bridge underestimated traffic demand
Plans for an Auckland harbour bridge were first hatched in 1860 by members of the farming community on the North Shore, then a sleepy backwater.
Engineer Fred Bell designed a drawbridge on floating pontoons, but the plans were deemed too expensive.
In 1928 another proposal was put forward, but it was 20 years later that pressure for new development space finally saw the Auckland Harbour Bridge Authority established.
In April 1954, after fierce lobbying, a loan of £5,002,000 (about $245 million in today's terms) was approved.
That produced the "austerity" bridge, with plans for a pedestrian walkway and a fifth traffic lane dropped.
During construction the decision was made to ban cyclists from the bridge, resulting in a protest from the New Zealand Amateur Cycling Association.
Workmen within a pressurised steel chamber excavating the seafloor for the bridge's caissons had to be "compressed" and "decompressed" so as to not get the bends.
A warning was issued to Auckland police and the public to treat suspected drunks with caution as they might actually be a worker with decompression sickness.
One motorist, stopped by who he thought was a drunk, refused to take the worker to the specialist medical unit at Westhaven. The bridge took four years to complete and was opened on May 30, 1959.
But by the early 1960s it became apparent that the bridge could not handle the amount of traffic needed.
Traffic flow was far above the royal commission's prediction the bridge would be carrying three million vehicles annually by 1965, with the volume exceeding 10 million that year.
A Japanese company won the tender to add two lanes on either side, and the added lanes became known as the "Nippon clip-ons", which were opened in 1969.
-Nicholas Jones
