Kāpiti's long-running Mackays to Peka Peka Expressway surface reseal project, costing $25 million, is expected to be finished by the middle of the year.
Contractors are busy removing large areas of the north and sound bound left lanes and creating a deeper asphalt seal to try and stop water from underneath penetrating it.
Work has ramped up recently but the NZ Transport Agency has been chipping away at the repairs since it became aware the surface wasn't peforming as well as expected after the road's opening in early 2017.
A total of 24.9 kms of repair work is required to the north and south bound left lanes of the expressway, NZ Transport Agency project delivery acting senior manager Tony Fisher said.
A total of 15km of repair work has been completed to date.
Mr Fisher said the north and south bound right lanes of the expressway do not appear to require repair works, however the agency continued to monitor those lanes.
He said as part of the initial investigations, the agency "identified that water was penetrating the road pavement, resulting in discoloration of the road surface and changes to its texture".
"The repairs require removing the surface of the road and reapplying a deeper layer of asphalt to increase the depth of the surface and reduce the ability for water penetration from beneath the road pavement."
Mr Fisher said he agency had repaired 8.9km of expressway throughout 2018 and in 2019, commenced the repair of the remaining 15.9km of repairs.
Due to the winter weather, repair work was suspended in July 2019 and recommenced at the end of September 2019.
Repairs are expected to be completed in June 2020 weather dependent.
The repair works were progressing well.
"The NZ Transport Agency acknowledges that there have been delays to the completion of the repair work due to poor weather conditions during the winter months, however we are satisfied that the work is progressing as quickly as possible."
He said, "The cost to repair the Mackays to Peka Peka Expressway is $25 million and is covered by the M2PP Alliance project."
The cost is being spread among alliance partners including the NZ Transport Agency, Fletcher Construction, Higgins and Beca, the agency said.