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 to week, 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.