A notoriously dangerous stretch of road between Pokeno and the Coromandel will be upgraded in a bid to reduce the number of crashes, though it may be 12 years before the work is complete.
The government will spend $278 million to upgrade State Highway 2 between Pokeno and the SH25 intersection.
In the past five years, 18 crashes along the 32km stretch of road have resulted in nine deaths and 25 serious injuries.
Transport Minister Simon Bridges said the two-lane road will be widened to three lanes, with two lanes for west-bound traffic heading to Auckland.
Median barriers and guard rails will be installed with the goal of reducing death and serious injury by 80 percent over the next 20 years.
Mr Bridges said an increase in road traffic, a rise the numbers of both domestic and international visitors and predicted future growth meant there was a strong case to make the road safer.
"Around 25,000 vehicles a day on the road and very significant congestion issues at peak times - and there are very significant safety issues that need to be addressed."
There may be an option to widen the road to four lanes in the future, he said.
"Evidence that NZTA [the New Zealand Transport Agency] put together on this really makes a case for two lanes northward-bound to Auckland, because the traffic is very concentrated on the way back and their data doesn't suggest it is on the way there. But we will keep the option open.
"And there will be passing lane improvements made on the way into the Coromandel.
Construction is expected to get underway in 2018 but work could take a further 10 years, Mr Bridges said.
The $278m investment was not new money from the government, but would come from NZTA's existing regional improvements fund.
"Of course that money and funding needs to be appropriated and spread around regional New Zealand but this is definitely a priority and I think people will notice changes, particularly at the northern end, quite soon."