If you can't go around or over it, the next option is to go under it: Once again the Government is considering a tunnel in the Waitemata Harbour.

For the past 60 years, the Auckland Harbour Bridge has been the main connection between the North Shore and Auckland's city centre.

NZ Transport Agency says traffic at the approaches to the bridge at morning and afternoon peak periods are at capacity with heavy vehicle use on the rise.

Heavy commercial vehicle use had increased 30 per cent over five years and was now approaching 11,000 movements on a weekday.

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However, the structural capacity of the bridge has been maximised and with projected growth looming the transport company is looking into multiple options.

Three separate transport options have been outlined in an NZTA report but even if one is decided upon, work won't start until the 2030s.

• Build a tunnel for light rail only.
• Build a tunnel for light rail and road access.
• Or, do nothing.

The report goes on to say when discussing the three options that there was no inclusion of heavy vehicle restrictions but added restrictions would likely be added in the future to manage the longevity of the harbour bridge.

Indications from NZTA in 2018 suggested a restriction of 35 tonnes was a possible scenario, but not set in stone.

The best option to reduce traffic in the city at morning peak times was a combination of road pricing and light rail, the report said.

"A light rail only crossing combined with road pricing delivers the best outcome for the city centre in terms of fewer cars entering the city centre during peak traffic times."

A road crossing with pricing would result in 3500 more vehicles entering the city centre during peak AM hours, compared to the light rail crossing.

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The report shows predicted congestion around a combined road and light rail crossing on the Waitemata Harbour
The report shows predicted congestion around a combined road and light rail crossing on the Waitemata Harbour

That would work against policies to reduce car trips and support a shift from private vehicles to more efficient models of transport.

The three proposed options were handed to Transport Minister Phil Twyford and Associate Transport Minister Julie Anne Genter in September.

The report highlights public transport use is showing "strong and sustained growth" but peak travel periods are increasing in the country's biggest city.

"Further development of this project should ultimately enable delivery of a multi-modal corridor across the harbour, with flexibility for rapid transit and road to potentially be delivered in separate tunnels at separate times."