After months of uncertainty, it seems the road from Ōtaki to Levin will be improved in the short-term, and a new road is being planned for the long-term. NZ Transport Agency say:
The NZ Transport Agency has released plans for the Ōtaki to north of Levin (O2NL) transport corridor to improve safety and resilience as well as planning now for future population growth. …

Work for a new two lane state highway will be progressed creating four lanes of capacity on the corridor along with the existing road. The new State Highway will allow for additional capacity in the future by protecting a route suitable for four lanes. …
In the short term, immediate safety improvements will be made on the existing highway.
“These safety improvements will initially focus on speed management, road marking, signs, and enforcement, followed by infrastructure measures.”
Public transport enhancements will be investigated for the region which could include rail connections, park and ride availability and bus service improvements. …
Sustainable land use, enhanced walking and cycling access and staging construction of the new road to manage heavy vehicles will also be considered.