State Highway 6 was extensively damaged after flooding in August. Photo: Waka Kotahi NZ Transport Agency
Roading crews are confident the major route between Nelson and Blenheim will be reopened before Christmas and the "busy summer season".
Waka Kotahi has reached the halfway mark of a seven-week closure of State Highway 6, between Hira and Rai Valley so emergency flood repairs can be completed.
The road has been closed since 1 November with crews working towards a week-before-Christmas deadline.
Severe rain which hammered the top of the South Island in August caused extensive damage to the road.
There are several serious underslip sites which have been excavated and had retaining wall anchors drilled into them.
Three of these areas require crews to significantly cut back the road before it can be built back up again.
Motorists have been travelling between Blenheim and Nelson by using SH63 through to Kawatiri Junction, then onto SH6.
A temporary, subsidised air service between Nelson and Blenheim has also been offered to locals during the seven week SH6 closure.
The transport agency is planning to have two traffic lanes re-established for the holiday season.
Waka Kotahi maintenance and operations manager for the top of the South Island Mark Owen said the work was not straightforward.
"It's a very tight programme," he said.
"Obviously the weather is a challenge, and as they've started to dig down there found some challenges with worksites.
"But the team are absolutely committed.
"We know that this is having a wide impact across the region. We know we want to get it open ready for the busy summer seasons."
The worse case scenario was the road was reopened to only one lane, but that would only happen if more severe weather hit the area before the deadline, Owen said.
"If we hit some really significant weather or hit a major hurdle, the risk is it may not be open to two lanes.
"If everything goes well, we're expecting that we'll be able to two lanes.
"But if we do have something that's really unforeseen, there is a small risk that we might only have sections which are a one-lane."
He acknowledged the impact the closure was having on residents and businesses.
"The detour we know is an extra hour of travel so that is a challenge.
"People that live in the area, we've made provision for them to get out via a forestry road.
"But we know through the Rai end side, it's having a big impact."