State Highway 4 near Upokongaro finally has two lanes open to motorists as work to fully reseal the road continues.
The road has been one lane for most of the past six years, after a 2015 slip washed away a significant portion of the road.
The new portion opened on Monday, with previous road now bypassed and the temporary traffic lights switched off.
Work on the road has been controversial, with concerns ranging from the strength of the original repair, to criticism from business owners around the length of time the repair was taking.
Work was done in 2017 - almost two years after the original slip - to fill in parts of the road. This repair was short-lived, when around 3m of that fill slumped back into the river.
Waka Kotahi NZ Transport Agency then decided to buy a nearby property so the road could be rerouted away from the slip entirely.
The purchase was finalised in January this year, and work to re-route the road began shortly afterwards.
Waka Kotahi confirmed late last month that current estimates show the six years of work have cost around $2.1 million, including buying the nearby property.
Ross I'Anson, Waka Kotahi Manawatu-Whanganui system manager acknowledged that the repair has been a drawn-out process.
"Following [the failed repair], we sought insurance for the repair and began investigations into other repair options," he said.
"We then completed a design for the current realignment, then undertook the extensive resource consent and property acquisition process before starting physical works. Throughout this process, we also worked closely with tangata whenua."
"We always endeavour to complete road repairs as quickly as we possibly can, however there are a number of steps we need to take to ensure we get it right and this takes time."
Sealing works will continue over the coming months, before Waka Kotahi then begins painting the road at the beginning of summer.