Work on resealing a lot of the Mackays to Peka Peka Expressway is a long way from being completed.

"To date, a total length of 5.4 kilometres of remedial work has been completed to an estimated cost of approximately $2.3m," the NZ Transport Agency has told Waikanae resident Chris Turver in response to a series of questions from him in regards to the sealing of the expressway.

But "an estimated length of 49 lane kilometres is currently expected to require treatment to remediate the risk of premature failure."

Moreover, "The resealing of the north and south bound slow lanes, and the fast lane remedial repairs are currently planned for completion by mid-2020."

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The 18km expressway, costing $630 million, was officially opened in February last year, but some months later minor fatigue of the surface began to be noticed.

It appeared the fatigue was caused by water penetrating the membrane seal that was applied to the pavement prior to the surfacing, meaning small particles had been loosened in the top of the pavement causing discolouration and texture changes.

The fatigue issues saw the agency start a resealing programme.

Mr Turver, a former Wellington Regional Council Kāpiti representative, who pushed for 10 years for Transmission Gully, the expressway, and rail electrification to Waikanae, said it was embarrassing the expressway project had failed so badly after all the positive glare of publicity.

"It's still a great new road for the country but the sheer scale of sealing failure raises many questions including who was responsible and who will pay."

Asked who was responsible for the sealing faults and who was paying for repairing the sealing faults, the agency said the Mackays to Peka Peka section of the Wellington Northern Corridor was delivered under an Alliance procurement model consisting of the NZTA, Fletcher Construction, Higgins and Beca.

"The M2PP Alliance partners are responsible for the delivery of the project and the remedial treatment of all defects.

"The cost of pavement repair works will be covered in accordance with the terms of the Alliance agreement."

To a further question of what the estimated final cost would be resealing almost 50 lane kilometres, the NZTA replied "the final scope for the repairs have not yet been agreed and it is still to be negotiated".

Mr Turver also asked the NZTA what action it had taken in terms of accountability to ensure workmanship of the standard seen on the expressway would not be repeated on other roading projects around New Zealand, particularly Transmission Gully.

The NZTA replied it was "standard practice for the Transport Agency to review its experiences and outcomes for all roading projects to ensure that lessons are learned and, where necessary, applied to future projects".