"Construction is anticipated to start between 2015 and 2019 and be completed between 2020 and 2025," was all it could say yesterday.
Highways manager Tommy Parker said the board would open hearings early next year in "a robust process that enables the Transport Agency to deliver the project as quickly as possible with the best value for money, subject to consents".
Campaign for Better Transport convener Cameron Pitches questioned the need for rushed consenting, given the agency's inability to pinpoint a startdate.
He urged it to take time to assess more cost-effective alternatives proposed by his group to improve the safety and efficiency of the existing main road north, such as adding passing lanes and building a Warkworth bypass.
"We think that would offer far greater value for money without all the environmental impacts a four-lane motorway is going to have."
But Labour transport spokeswoman Darien Fenton, whose party vows to cancel the project and free up construction funds to accelerate Auckland's $2.86 billion underground railway, called the hurry-up-and-wait consenting process "quite cynical".
Greens transport spokeswoman Julie Anne Genter suspected the hold-up was to do with a longer lead time for forming a public private partnership for the project.
• Information open days - Orewa Arts and Events Centre, 4pm-7pm, November 28; Shoesmith Hall, Warkworth, 10am-2pm, November 30.
Northern Motorway extension
• 18.5km from the Johnstones Hill tunnels south of Puhoi to just north of Warkworth
• $760m: Cost of the extension
• 2015-2019: Construction start - between 2015 and 2019