The divvying up of costs for the billion-dollar Pūhoi to Warkworth motorway will not be finalised until next year.

The road opened last year, but the NZTA Waka Kotahi is still fighting with its builders, a Fletcher alliance with Spanish giant Acciona.

The transport agency says the binding and confidential disputes process will not finish until the second half of 2025.

"The parties [are] in the process of agreeing the inputs into the determination process," it said.

It has already paid tens of millions in costs, due mostly to Covid disruptions.

The motorway - built as a public-private partnership - is open, but has not been signed off.

The agency said 115 tests are being done to certify it is up to scratch, such as ensuring that the sloping sides meet a 100-year design life.

This story was originally published by RNZ