The Manawatu Gorge should be open in just over a month if work at the slip-hit site stays on track.
New Zealand Transport Agency's Palmerston North state highways manager David McGonigal said contractors had worked around the clock where possible and the road rebuild was advancing well.
"From week toweek, the troops are putting in the hard yards, and they're making real and visible progress, every day and every night," Mr McGonigal said.
He said contractors were rebuilding a number of different structures simultaneously.
The main bridge - near the Woodville end - is being completely rebuilt into a new three-span bridge 60 metres long.
Towards Ashhurst, a destroyed half-bridge is being replaced with a new retaining wall to secure the new road in place.
At the far Woodville end, the existing half-bridge escaped damage from last year's huge slip, but work is continuing with bridge beams and piles being constructed to tie in the existing highway to the new 60m bridge.
Mr McGonigal said what the crews had achieved in planning, designing and rebuilding the structures in such a short timeframe was remarkable.
