"Mr Gammie came to a view on his own that he would like to go. I think it was becoming very hard for him because, unfortunately, we were getting asked considerably about his future.
"There is no doubt he's going and it will allow some fresh air to be found and it will be easier for people to get on with what they're meant to do, no question."
Stiassny told the select committee it was likely a number of other people at the agency would also decide to leave.
"I have made it very, very clear in my statements that accountability should not stop with Mr Gammie. That would be unfair in my opinion.
"There are a lot of people who should share in the responsibility for this, and it is wide-ranging."
Stiassny named the Auditor-General's office, auditor KPMG, the Ministry of Transport as among the parties with a "share in this".
"But that has to come out in the reviews."
Talking afterwards about the case of Geoff Dale, an Auckland pensioner left out of pocket after his restoration work on a rare car was overseen by a now suspended vehicle inspector, Stiassny said it was unfortunate.
"That is unfortunate for that gentleman but we do have to come back to what we are trying to do. What we're trying to make the roads safer and to ensure that they are safer.
"There will be some consequences to that. It's sad that a man has lost $15,000 but unfortunately that is just one of the consequences, but it's a lot better than another life being lost," Stiassny said.
Gammie announced earlier this week that he had resigned, saying he was a distraction to the review and improvement of the regulatory function at the NZTA.