Plans for a second harbour crossing near the Auckland Harbour Bridge are likely to be made public next year.

Wayne McDonald, Transit NZ's regional manager for Auckland, said it was investigating options for a bridge or a tunnel under the Waitemata Harbour and tunnel connections to the Northwestern and Southwestern Motorways, costing up to $2 billion.

A brief was being prepared for consultants to investigate the options for a second crossing near the existing bridge, which carries up to 160,000 vehicles a day.

Transit is keen to secure a route and land by 2004 but construction is unlikely to start before 2010.

The planning process and design work are expected to take several years.

A second crossing must also fit plans to widen the approaches to the harbour bridge at St Marys Bay and any tunnel must fit plans for the extension of State Highway 20 through Avondale.

Meanwhile, the Victoria Park flyover, a notorious bottleneck, has developed "concrete cancer".

Transit said it presented no danger to the 90,000 vehicles which used it every day.

"It doesn't crash, go bang and just drop on the ground," said Mr McDonald. "It's like your bones over your lifetime. They get weaker and weaker."

Concrete cancer is a term for ageing concrete structures that begin to break up when reinforcing steel rusts or because of a chemical reaction among lime and silica in the original mix.

Moisture inside porous concrete is usually the cause of the problem.

Transit has been cutting faulty spots out of the flyover and replacing them with new concrete for more than 10 years.

Mr McDonald said it received engineering advice and assurances that there was nothing to be alarmed about.

He said concrete cancer on Auckland's motorway network was limited to the 40-year-old flyover, which was built to a safety factor two-to-three times the maximum load and still had a life of 20 years.

The former Orewa River bridge, built in 1935 and replaced a few years ago, also developed concrete cancer and never posed a danger to motorists, he said.

The St Marys Bay Association is opposed to plans by Transit to increase the flyover from four to six lanes and is promoting a more expensive option to build a trench to bury the 1.3km motorway stretch from Victoria Park, past St Marys Bay to the Harbour Bridge.

Transit has agreed to include the trench in a range of options going out for public consultation in February or March.

Options for widening the flyover could result in the demolition or removal of the Birdcage Tavern at the bottom of Franklin Rd.

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