"I reinforced my support for the Road to Zero programme but did ask more caution was exercised around this kind of expenditure and we just consider whether it's strictly necessary as we move forward.
"I provided my views to Waka Kotahi that while they make the spending decisions at arm's length from the minister, I do expect them to exercise a bit more caution in the future."
He said Waka Kotahi had not misled the ministry, and he did not want to discourage it from spending on the campaign overall.
The Road to Zero campaign aims to reduce deaths and injuries from vehicle crashes, in part by making smaller, cheaper improvements like median barriers to the nation's more dangerous roads rather than focusing solely on expensive new ones.
The money for the large props came from the $4.7 million fund set aside for the campaign.
"We're investing in $2.9 billion on Road to Zero over the next three years, so this expenditure was a very small proportion of that," Wood said.
"Most of the money goes into improved roads, improved traffic policing, and things that will keep us safe, and we do need to invest in a strong public campaign to change attitudes and behaviours and I think most people would understand that. But just as we go along, we need to make sure that it feels proportionate and appropriate and that's what I've asked Waka Kotahi to consider."
He said other public awareness efforts like the "Ghost Chips" TV ads and anti-drink-driving campaigns had been successful in the past, and he did not want to discourage agencies from trying to deliver on their core business.
National's Simeon Brown said Michael Wood needed to apologise for the spending.
"This symbolises the wastage we are seeing across government departments and that New Zealanders are sick and tired of in a cost of living crisis. Every single dollar should be respected as if it was his own."
Brown said promoting road safety was important, but it was at its most effective when it had a clear educational message, for example about not speeding.
"But spending $30,000 for a bunch of red zeroes that light up is a significant waste of taxpayers' money at a time when Kiwi families are doing it tough due to very high inflation and rising interest rates.
"The zeroes are not even about road safety. They are about telling everyone about the Government's policies, rather than knuckling down and doing the hard work," Brown said.