Recent wet weather and high river levels have forced a two-day closure of the Manawatu Gorge, to allow engineers to firm up and move the temporary highway further "inland" to protect it from potential erosion.
New Zealand Transport Agency's Palmerston North state highways manager, David McGonigal, said the temporary road, which had been in use for a month, needed to be re-routed to a more "resilient" location and that would take about two days' preparation work.
He said there had been some erosion of the slope on the river side and there was a need to provide more security to motorists and to protect the area from further erosion.
Completion of a section of bridge construction work had freed up more room for engineers to shift the route away from the river side.
While the existing road was secure, and there were no safety concerns, the move would help "future-proof" the area against storm events over winter that could eat away at the slope that was helping to support the road, he said.
The road will be closed at 8am today and will remain closed until 6pm tomorrow.
While the closure is in place, motorists will need to revert to using the alternative routes both day and night.
Electronic information signs will communicate the closure information to motorists, who are asked to observe the signs at all times.
"It's great to be able to move the road closer toward its final resting place, as it gives us a really good buffer, helping us stay one step ahead of Mother Nature," Mr McGonigal said.
"We appreciate the temporary closure is an inconvenience for people but the upshot is that it might help prevent a longer closure if a storm hits because it makes the road more secure and resilient."
Mr McGonigal said the closure would also enable work crews to advance the bridge construction work.
"The bridge crews will be able to pick up the pace while the road is being moved, which kills two birds with one stone and speeds things along."
Despite recent bad weather, progress was going well, he said.
While NZTA thanked the majority of motorists who were using the gorge responsibly, a small number of motorists had been seen speeding and overtaking after exiting the bridge construction zone.
"It's important for everyone that the gorge operates safely at all times and a few motorists are putting their fellow motorists at risk by speeding or carrying out dangerous overtaking manoeuvres, particularly at night.
"We've had people coming out of the construction site overtaking long lines of vehicles, and this needs to stop.
"We ask that people think twice and give safety the benefit of the doubt at all times."