A mix of technology and human errors converged to temporarily shut down Auckland's biggest CBD parking building on the city's busiest holiday of the year.
The council agency closed the nearly 2000-space building as Aucklanders flocked to waterfront events on Anniversary Day on Monday.
In another incident for the iconic Downtown Carpark, a block back from the CBD waterfront, AT had to raise the exit barriers on Sunday night after huge queues of concertgoers trying to pay became a problem.
On Monday, motorists arriving at the building around midday found the steel gates pulled closed.
Auckland Transport said at the time this was standard procedure when the building filled up, but RNZ saw many empty spaces.
On Wednesday, AT's group manager of parking and compliance, John Strawbridge, said the "smartparking" software did not recognise that Monday was a public holiday, and that spaces reserved for private leaseholders on business days, should be available to the public.
He agreed that motorists circulating inside the building might have avoided the vacant spaces, each of which displayed a red light - that turns green when available for use.
"That would absolutely be the situation, I'd be the same, I'd go in and see reserved and think 'oh jeez I probably can't use that'," he said.
A second IT system also measures the number of spaces available. The Skidata system includes the pay stations, barrier arms and tells electronic signs at the carpark entrance and on approach roads, when it is full.
No full signs were on display during the shutdown, and the system can be over-riden manually.
"My sense of it is that our guys should have put a little old-school sign out the front of the building as well, they didn't do that so that's certainly on us," Mr Strawbridge said.
No staff 'on the floor' for waterfront event
There were different problems at the parking building on Sunday night.
The building was full due to an evening concert on Captain Cook Wharf staged by council-owned Ports of Auckland, with an estimated 14,000 audience.
Long queues of angry parkers queued at all of the buildings pay stations after the 10pm ending, reaching a point where AT staff decided to raise the exit barriers and let everyone out free of charge.
On that evening, no staff were apparent "on the floor" and the staffed ticket office was closed.
AT said motorists can prepay on arrival during the flat-rate evening, weekend and holiday periods, but it "involves some maths".
There are also no obvious instructions on the machines about the pre-pay option.
RNZ asked Mr Strawbridge why there were not more staff on during scheduled big events, to help guide motorists to available parks.
He said that raised questions of how many staff would be needed, and where would they stand that would not cause health and safety problems.
Auckland Transport said it would investigate the parking building software before next Tuesday's Waitangi Day holiday.