A builder of the much-delayed Transmission Gully motorway project north of Wellington has gone to court seeking $75 million from the engineer alleging "defective" designs when costing the project.
The $1.2 billion, 27km project was supposed to open this week but there is currently no completion date due to this year's lockdown.
The project has blown through previous deadlines and is hundreds of millions of dollars more expensive than initially budgeted for.
Court documents show some of the members of the consortium in the public-private partnership are embroiled in court action.
Builders CPB Contractors (and HEB Construction) are seeking $75 million from engineers AECOM New Zealand alleging a "breach of contract", and "misleading or deceptive conduct".
The entities together won the tender, and the documents show the builders allege there were "material differences" between the tender design and those produced later.
The builder says errors in design work on bridges and drains meant it had not been able to properly estimate how much it would cost to build.
It says it would have submitted a higher tender to the Transport Agency Waka Kotahi, or it would have amended the design or reduced the scope of works.
Separate court documents show that in March last year the parties were still exploring the possibility of an alternative dispute resolution.
Any hearing is likely two years away and pleadings may yet change.
If the case does go ahead it could take up to 10 weeks.
Waka Kotahi has previously paid the builder $190 million over resource consent delays and a separate $164m for delays due to last year's Covid-19 lockdown.