Auckland leaders look likely to use Government arguments for completing their motorway network as ammunition for building a $2.4 billion central city rail tunnel.

Officials lined up with Auckland Council transport committee members yesterday in describing the tunnel as a "strategic fit" with the Government's aspirations for turning the country's largest city into an internationally competitive economic powerhouse.

They warned that without it, the city's roads and railway lines would become clogged by 2024, when there would be no spare capacity left for trains and buses, let alone more cars.

Auckland Transport stakeholder manager Stephen Rainbow, leading presentations by officials from his organisation and the council, said it had always been envisaged Britomart Station be opened into a loop tunnel after rail electrification.

He compared the completion of the western ring motorway route, which the Government is backing to the hilt with $2 billion of new investment, with what he saw as a critical need to complete Auckland's rail network.

Transport Minister Steven Joyce said last week that a Government review had found a glowing business case for the rail tunnel seriously lacking in substance, although he agreed to let the Auckland Council safeguard the 3.5km route at its expense.

But Dr Rainbow said the tunnel, which would create a loop through Britomart with the western and southern rail lines, was "not just some folly dreamed up by traffic engineers as the next big capital project in the city."

"It's been envisaged for years and years and years that Britomart would be pushed through and that this critical final link in the rail network would be completed to optimise rail in this city."

He indicated that an important change since the tunnel business case was prepared last year for KiwiRail and the former Auckland Regional Transport Authority was earthquake damage to Christchurch.

"Christchurch is probably going to take at least a decade to rebuild," he said.

"With Wellington's economy static, Auckland's economy and particularly its business basis in the central city is critical to the future of this country."

Councillor Chris Fletcher, a former National Party minister who as Auckland City mayor from 1998 until 2001 ensured the construction of Britomart, said even Mr Joyce had acknowledged to her that the tunnel was "a logical strategic fit."

Auckland Council chief planning officer Roger Blakeley said the Government would not realise a full return on its $1.1 billion rail electrification investment without completing the central city link.

Mr Brown said in his 16 months of mayoral campaigning across the region, 95 per cent of people had complained about transport problems "and how the hell are we going to unclog the roads and reopen this city."

"The first project I put to them was not a roading project, but the inner-city rail loop, and they said: Get that job done, it's 60 years overdue."

The committee decided a report on funding and regulatory aspects of the rail link should go to the council's governing body. That followed details from staff of five work streams to be overseen by a committee of council chief executive Doug McKay, Auckland Transport chief David Warburton and Transport Agency northern director Stephen Town.