A congestion charge will be considered for Auckland but it would be unfair to sting people without providing alternative transportation, the Green Party says.

The Automobile Association has also warned against letting the city stall while an investigation gets underway into "smarter transport pricing" for the growing city.

Terms of reference have been set out for an inquiry, more than a decade after the government first examined the idea of a road pricing system.

A road user pays system or congestion charge are among the ideas to be considered according to Transport Minister Simon Bridges who announced the project on Wednesday.

He admits it could be years away given the need to consider various options and hone down to one specific idea for Auckland.

"It's a long term thing here ... I think realistically that will take not months but years," he said.

"I think the honest truth is we don't know (how long). Firstly we don't know if it will happen."

The process will take into consideration the cost to households and a pricing system not about revenue raising.

He has promised a "transparent process" of discussion around peak and off-peak pricing and a reduction in the petrol tax and road user charge to ensure it was revenue neutral.

Green Party transport spokeswoman Julie Anne Genter wants reliable, fast and affordable public transport before any new charge is implemented.

"It would be incredibly unfair to sting people in the pocket for driving into Auckland when there is simply no other option for them," she said.

There are also concerns that a congestion charge or other road price offers only a long-term solution.

Automobile Association infrastructure advisory Barney Irvine wants to see a weighted cost-benefit solution sooner.

He's worried traffic conditions will become "unbearable" before congestion charging or an other solution is introduced.

A shorter-term solution according to Auckland Mayor Phil Goff, who hinted at the announcement on the weekend, would be a revenue sharing arrangement with the government.

As happens in Australia he wants to see a percentage of GST devolved from the government to help Auckland raise revenue for new transport infrastructure.

For the longer-term he backs a road pricing system.

"With 800 extra cars on Auckland roads each week and 45,000 additional residents in our city each year, radical changes need to be made to stop our city grid- locking," he said.

After agreement between the government and Auckland Council the first stage of the investigation is expected to be completed by the end of the year.

The investigation comes 13 years after the Ministry of Transport first investigated road pricing for Auckland, resulting in a 2006 report considering several schemes.