The government is promising more improvements to SH1 south of Whangarei, including a possible bypass of the Brynderwyn Hills.
Contractors recently completed an $18 million job on the north side of the hills, realigning the highway and installing wire barriers to reduce crash rates.
Work has also begun at the Auckland end of the highway to carve a new route for the Puhoi to Warkworth extension.
The Transport Agency said further projects were in the pipeline, including two options for a bypass of the Brynderwyns to improve safety and cut costs for heavy vehicles.
Transport Agency design manager Brett Gliddon said about 2 million tonnes of freight per year moved between Auckland and Northland, and tourism in the region was worth $1 billion annually.
Construction was due to start in 2019 on improving the winding stretch between Whangarei and the Port Marsden turnoff, he said.
"Upgrading this section of highway to four lanes ... will reduce the high number of fatal and serious crashes ... and provide a more reliable freight connection to the port.
"Options include upgrading the existing road to a four-lane expressway; upgrading the southbound lane and building two new lanes to the west for northbound traffic; or building a whole new four-lane expressway, to the west or east of the current highway."
NZTA is asking for community feedback on its plans at open days this month in Whangarei (19 August, Whangarei i-SITE), Mata (17 August, Mata Hall) and Kaiwaka (15 August, Kaiwaka Hall).