The Transport Agency, in its briefing to Mr Bridges as the incoming minister, points to a risk of the Government not being involved in the ground-floor of the project. It called the council's timetable for enabling works as "sensible sequencing" to minimise disruption to the CBD.
The council is budgeting $250 million for the work to coincide with a major redevelopment of the shopping centre and for initial tunnelling to be completed before the World Masters Games comes to Auckland in April, 2017.
"We think this is a sensible sequencing of enabling works which will minimise disruption of critical intersections in the CBD and enable compliance with the planning conditions that only one intersection can be out of action at any one time," it told Mr Bridges. "A more compact construction schedule at a later time would prove too disruptive."
It also discussed a possibility of the major construction phase, of tunnels to Mt Eden and the construction of two underground stations, starting as early as 2018 - and being completed by 2022 for around $2 billion.
"The risk of not being involved in these early stages is that the key elements of the project get determined in the meantime," the agency said. "If the Crown is to be a future funding partner, it needs a mechanism to identify options and risks around planning, design, procurement and financing."
It suggested to Mr Bridges a possible role for itself as a technical partner with Auckland Transport in developing the project, to help to "manage Crown risk".
It also highlighted its experience in complex infrastructure undertakings of the scale of the rail project.
Mr Bridges acknowledged the agency's concern, given its belief that it had the country's foremost expertise in major transport ventures.
Transport Minister Simon Bridges said he was considering whether to approve Transport Agency involvement in "enabling works" from 2016. Photo / NZME.
"So if the council decides to build earlier than 2020, it may be desirable for NZTA to have input into the process, given the Crown will ultimately be contributing to the funding," he said.
Mr Brown said he welcomed the agency's advice, and in particular its support for "sensible sequencing".
Labour's transport spokesman Phil Twyford said the Government was out of step with a groundswell of support for the City Rail Link.
Gateway tolls to last nine extra years
Motorists will have to keep paying to drive on Auckland's Northern Gateway for nine years longer than expected, the Transport Agency says.
The Government body previously hoped that by 2045 tolls would pay off a $180 million loan raised towards the full $356 million cost of the 7.5km motorway extension from Orewa, the Johnstone's Hill tunnels.
But in briefing papers to Transport Minister Simon Bridges, made public yesterday, it has forecast an extended payoff period - to 2054.
The agency set up a national tolling scheme to administer billing for the road. It hoped other schemes would soon be brought into the fold.
That idea suffered a setback when the former Labour-led Government abandoned plans to charge tolls on Tauranga's duplicate harbour bridge to secure New Zealand First support as a coalition partner after the 2005 general election. As a result, administration costs are still chewing up 34c of every $1 raised in tolls.
Those costs are expected to be brought down once the $455 million Tauranga Eastern Link road opens next year, and motorists are tolled to drive along 17km of its 23km route.
Auckland Council is also considering whether to charge drivers $2 or more to drive on the Super City's motorway network to close a $12 billion transport funding gap. Although 2.77 million trips were made on the Northern Gateway road in the six months to December, Transport Agency spokesman Andy Knackstedt said traffic volumes remained below what was forecast before it opened in 2009.
