A high-tech transport project that ran into problems with its Silicon Valley partner has already cost the government more than $5 million, but another $19m will be put into it.
The Transport Agency pulled out of its partnership with US firm Machine Zone after testing two transportation apps in Queenstown and Auckland.
This first phase of its Mobility as a Service project cost $5.5m against a budget of $5.05m.
The business case for what was a risky project was much less detailed than would be expected, a review by Deloitte said.
The first phase focused on building apps, but that approach has now been ditched, even though NZTA has previously talked up the results of the two trials.
"It's important to understand that the Mobility OS (operating system) programme is about much more than developing apps," the agency's general manager of operations Charles Ronaldson said in a statement.
The agency refused to say what Machine Zone, now called MZ, and other contractors were paid.
It dropped the US technology last September and is now developing its own in phase two, which has a budget four times higher, at $19.5m over two years.
This includes expanding its data collection from CCTV and street-side sensors, and building a software engine that could predict traffic movements.
Phase two was much more closely controlled than phase one, which was run by NZTA's trouble-plagued Connected Journeys unit, NZTA said.
A Deloitte review of Connected Journeys said the business case for phase one was much less detailed than expected "for a substantial technology project that has elected to take a higher risk than normal approach to delivering the solution".
"While the proposition may be valid, it does not appear to have been rigorously tested prior to funding being approved despite conducting pilots in Queenstown and Auckland," Deloitte said.
It also questioned NZTA taking on the fast-moving Google and Uber in trying to offer journey-planning solutions to travellers.
"The likelihood of widespread uptake of an NZTA developed Mobility as a Service mobile application must be decreasing."
Deloitte recommended the agency use the technology to push the likes of walking and public transport.
NZTA said it was not trying to replicate others' services but could "help the private sector provide more accurate and consistent travel information to people through their products and services".
"We are continuing with this work because it has the potential to significantly improve the quality and the accuracy of the real-time travel time information which New Zealanders use every day," Mr Ronaldson said.