The board also could not be reached for comment and NZTA said no further comment would be made.
Meanwhile, mystery surrounds the situation of KiwiBuild chief executive Stephen Barclay, after the Weekend Herald revealed he had not been at work since early last month.
Neither Prime Minister Jacinda Ardern nor Twyford, as Housing Minister, would be drawn on Barclay's circumstances.
The new Ministry of Housing and Urban Development issued a brief statement today saying Barclay had not resigned but not provide any background.
"Stephen Barclay has not resigned. While he is away from the office, Brad Ward is providing operational support for KiwiBuild. The ministry will not make any further comment," the statement said.
At her post-Cabinet press conference this afternoon, reporters grilled Ardern about Barclay but she revealed little other than to say it was best characterised as an operational matter.
"There is not much more than I can say on it. It's appropriate that this remains with the public service, and they are dealing with that."
Arden said it had nothing to do with the KiwiBuild policy or the implementation of the KiwiBuild programme.
Asked if it was a personal matter, Ardern said: "I won't say anything beyond that."
Speaking on TVNZ's Q&A programme last night, Twyford also would not provide any details.
"I can't comment on anything to do with an individual public servant, that would be completely inappropriate," he said.
"I don't hire the public servants – they are not my responsibility to manage. I simply get advice from them."
Although the Government is keeping its distance from what it calls operational issues, officials are often brought in, as in the case of the NZTA scandal, to answer difficult questions when bad news is being delivered.
Immigration Minister Iain Lees-Galloway had Immigration New Zealand deputy chief executive Greg Patchell at his side when he held a press conference late last month to announce he had changed his mind in the case of Czech drug smuggler Karel Sroubek.
And it was director-general of Health Ashley Bloomfield who took questions in the Beehive theatrette last month over a plan for a regional vaccination programme against meningococcal disease in Northland before Ardern and Health Minister David Clark entered.