The witness called the driver a bit of a 'd**khead' saying it seemed he "thought he was above anyone else".
It is understood the NZTA driver reversed into the two car parks and then got out of the vehicle to go to the bathroom.
The witness and a second person tried to confront the driver of the car once they came out of the bathroom but failed.
"[The driver] didn't even acknowledge us."
A Waka Kotahi spokesperson said they will follow up with the driver and would remind staff to "be mindful of parking considerately in future".
It's not the first time bad parking has been in the spotlight.
Cameras were this month installed in Christchurch to catch bad parking behaviour.
Council transport operations manager Steffan Thomas said Hereford St, near Oxford Tce, was swamped on weekend nights and the rule-breaking was sparking concerns.
"With the high volumes of people, we need to make sure that they can arrive and leave safely and recently we have had issues with people double parking or parking in the taxi and rideshare spaces.
He said if people do choose to park in the wrong space, it will be picked up by the cameras and they can expect to receive a ticket in the mail.
