Transmission Gully will not be open before Christmas, despite the Transport Agency Waka Kotahi putting the pressure on its contractor to meet the target.
Board chair Sir Brian Roche said the delay was extremely disappointing and frustrating.
"We have been pushing very hard for the Transmission Gully motorway to open to the public as soon as possible and we made our expectations clear to WGP [Wellington Gateway Partnership] and CPB HEB [joint venture] that we wanted this to be before Christmas.
"With many outstanding issues yet to be addressed, tests to be met and consent tasks to complete, there is a lack of sufficient assurance that road opening pre-Christmas is achievable."
He said it may be "some time" before all the safety and quality assurance tests required in the contract were met.
As at 10 December, out of 100 safety and quality assurance tests, 41 final test submissions had been received from the builder CPB HEB, of which 34 had been accepted by the Independent Reviewer.
Of the 45 consent tasks that need to be completed as at 3 December, 17 had been completed, 26 were underway and had been progressed to varying degrees.
Waka Kotahi Transport Services general manager Brett Gliddon said the agency had been working with WGP and CPB HEB to try and get the 27km road opened as quickly as possible.
The road was due to open by 27 September 2021, following an agreement for additional time and compensation due to delays caused by the Covid-19 lockdown in 2020.
There was already significant risk that WGP and CPB HEB were not going to meet this date prior to the August 2021 lockdown.
Waka Kotahi is currently in commercial discussions to determine how much of the delay is due to the most recent lockdown and other Covid-19 restrictions, and the financial implications of this.