Waka Kotahi says repairs on State Highway 1 through the Brynderwyns need to be carried out before winter.
The main route in and out Northland needs to be completely closed for a number of months for recovery and rebuild work after suffering significant damage in various extreme weather events this year.
There is $62 million earmarked for the job, but dates are yet to be signed off with businesses worried the closure will mean a big economic hit.
An independent report put the cost of an earlier closure of the Brynderwyns at almost $2m a day.
Listen to the interview
Waka Kotahi regional relationships director Steve Mutton said the agency had delayed the work so it could consult with local communities.
Work on SH1 on the Brynderwyns had been going on since Cyclone Gabrielle, which caused significant damage to the connection between Auckland and Whangārei, he said.
The work needed to be done to ensure the route could withstand any weather events this coming winter, he said.
"So to date the work's really been focused on the short-term emergency response which made sure that the route was open as quickly as we could, safely and efficiently for people to use that critical link."
But urgent repairs were now needed to return the road back to a pre-cyclone condition, Mutton said.
"So now we're actively working with the people of Northland on a way forward to make sure that we get their feedback and they can inform our next steps."
Asked how urgent the work was, Mutton said the weather over the last year had been very unfavourable for Northland.
"We've just got some concerns there around some overslips and hills are still moving, we've still got some concerns around some of the retaining walls around the edge of the road.
"So it's important that we get in there and we shore that up to make sure it can last through this next winter period, (during) which we know more rain will come."
Deciding when to close the road to get the work done was challenging, he said.
"We really understand and acknowledge the impact that this closure will have, this proposed closure will have on businesses and the local community."
That was why further consultation was being done on the best timing for the work, he said.
"It really involves balancing the need to complete these works during the drier warmer months while meeting the needs of the businesses and the people in the local communities."
Tourism and freight needs such as for the kiwifruit industry were two important considerations, he said.
When the Brynderwyns closed it was important that any alternate routes were fit for purpose and Waka Kotahi had been working with the local councils to ensure that any alternate routes were safe and could deal with the expected amount of traffic, he said.
Mutton said it was important to make the decision quickly in order to give people as much notice as possible as to when the closure would take place.
The decision should be announced before Christmas, he said.