Auckland drivers will be hit with increasing midday traffic jams when current road improvements erode in 20 years, the Ministry of Transport says.

The Government began an investment programme for Auckland's transport infrastructure in 2002, which in the next four years will include the completion of the city's motorway system and the commuter rail upgrade.

The changes are expected to reduce congestion by about 14 per cent by 2021, despite a predicted population growth of 22 per cent.

However, in a briefing to Transport Minister Gerry Brownlee, the ministry said the city's road network was expected to deteriorate after 2021, with the improvements from the current investment programme having eroded by about 2031.


"Congestion will increasingly affect the midday period, and therefore business and freight travel, particularly after 2031," the briefing said.

"Public transport and walking and cycling trips are forecast to increase substantially, but together are forecast to account for less than 30 per cent of morning peak travel in 2041."

The briefing, released yesterday, identified Auckland and the upper North Island as key areas for investment.

Auckland was expected to account for 60 per cent of the country's population growth to 2030, and freight growth would be concentrated in Auckland, Waikato and Bay of Plenty regions.

A draft plan has been developed by Auckland Council to tackle the city's population growth problems by focusing new developments in the city's urban area.

It emphasises a shift to public transport and proposes $22 billion of spending on major Auckland transport projects over the next 30 years.

The briefing said the plan would mitigate the issues associated with the climbing population but would not resolve them.

"Even with a more compact urban form and higher fuel prices, private vehicle travel is forecast to increase from around four million trips per day in 2006 to around 5.5 million trips per day in 2041."


The plan also raised a number of issues for the Government, including a $10 billion to $15 billion funding gap between the cost of the plan and revenue expected to be gained from current sources, the briefing said.

Another concern was that the plan did not take into account the predicted increase in congestion on the state highway network.

Auckland Council was expected to propose some form of road pricing scheme to raise funds, and the briefing advised that the Government would need to consider a number of operational and policy issues surrounding such a scheme, including community support.

"Road pricing incurs high collection costs as a percentage of revenue. It might be an effective mechanism for managing demand and alleviating congestion, but it is not currently an efficient way to raise revenue," the briefing said.

The ministry said there was no need to rush a decision on future Auckland transport funding.

"The effectiveness of recent investments means there is a short breathing space before decisions need to be made on the next generation of major projects."

Auckland Mayor Len Brown said the briefing paper "reinforces the concerns Aucklanders have felt for too long".

Building new motorways was only a part of the solution - without major investment in public transport, new roading projects could only move the congestion an exit or two down the motorway, he said.

"We have to provide choice in transport to keep Auckland business moving. I'm committed to working with the Government to make sure this happens."

Council transport committee chairman Mike Lee said the National Government had been in denial about Auckland's transport problems - showing a bias for building rural roads instead of the rail link.

* Changes to Auckland's transport infrastructure are expected to reduce congestion by about 14 per cent by 2021.
* Auckland's road network expected to deteriorate after 2021, with improvements from current investment programme of $22b to have eroded by about 2031.
* Congestion will increasingly affect the midday period.
* Public transport, walking and cycling trips forecast to increase but account for less than 30 per cent of morning peak travel in 2041.
* Private vehicle travel forecast to increase from four million trips a day in 2006 to 5.5 million trips in 2041.