Truck drivers say moving Auckland’s port to Northport near Whangārei would add an extra $1 billion to the cost of moving goods around the country.
A report by the National Road Carriers Association says moving the port north would also increase emissions and add to congestion.
Multiple reports have suggested the port should be moved and the proposal is a bottom line in the confidence and supply agreement between New Zealand First and Labour.
National Road Carriers Association (NRC) chief executive David Aitken says while it would increase business by five-fold, the costs outweigh the benefits.
The report finds heavy truck traffic would increase, particularly on roads around the proposed Swanson road-rail inland port and across Auckland.
It says Auckland’s business growth is moving south, and with the golden triangle of Auckland, Waikato and the Bay of Plenty dominating economic growth, Whangārei is too far away.
Around 340,000 heavy truck trips and 27,000 freight trains would be needed to carry containers and goods from Northport to the proposed inland port at Swanson.
Other concerns include travel time, competitiveness and sustainability.