It is also keen on Auckland Transport building a link from the end of the motorway across the top of Warkworth to intersect with Matakana Rd, diverting holiday traffic from the intersection, although the council body could not say how much that would cost.
Despite allocating $600,000 for route investigations, Auckland Transport does not expect anything to happen before 2021.
Transport Agency highways manager Tommy Parker says upgrading the intersection in the meantime would add too much disruption.
"We estimate construction could take two summers to complete and that will mean considerable disruption for everyone - children from the nearby [primary] school, residents, local businesses and road users," he said.
Auckland Council member Penny Webster, a former Rodney District mayor, supports a link road and agrees with the agency that upgrading the intersection now would prove too disruptive.
But Rodney Local Board member Greg Sayers predicted last week at a gathering of frustrated residents at the intersection that the agency would disown it once the motorway opened. No longer part of State Highway 1, it would become Auckland Council's problem.
Karen Sollitt, who lives just north of the intersection, said she preferred to stay home at holiday weekends rather than battle the tide of traffic.
Warkworth Area Liaison Group co-chairman Bruce Manson said the agency's decision breached a memorandum of understanding in 2006 that envisaged an upgrade being completed by now.
"It is one of the most ill-designed and most frustrating intersections in the country," he said.
"It's the local people who are forgotten in this. They are the ones who put up with it on a daily basis, but people travelling north and south at weekends and holiday weekends know what it's like when you get a 20km backup of traffic which is totally the result of the problems at Hill St."
Snells Beach Residents and Ratepayers' Association spokesman Bryan Jackson said his community strongly supported the motorway extension, and he acknowledged a northern link road would take some heat off the intersection.
But Snells Beach's population was earmarked to treble to about 12,000 people over 30 years, and getting through Warkworth would become even more nightmarish without an upgrade.
Hill St intersection
*State Highway 1, Hill St, Matakana Rd, Sandspit Rd, Elizabeth St.
*Average weekday traffic: 19,776 vehicles.
*Average weekend daily traffic: 27,633 vehicles.