Freight movements eased slightly last month as the country moved into the Covid-19 traffic light system.
The ANZ Bank's monthly Truckometer index showed heavy traffic movements - a real-time measure of current economic activity - decreased 0.6 percent in December.
The bank's chief economist Sharon Zollner said heavy traffic was not far off pre-Delta outbreak levels.
"Heavy traffic is the more useful indicator in these strange times. Over (the fourth quarter) as a whole, the index was up 5.3 percent. This is consistent with our early Q4 GDP (Gross Domestic Product) pick for a 2.5 percent increase."
Heavy traffic moved roughly twice as much as GDP, she said.
"This represents a partial bounce-back from the lockdown-induced 3.7 percent fall in GDP in Q3."
However, light traffic, which points to activity six months ahead, was up nearly 16 percent as the Auckland border opened.
"Both traffic and other economic data are going to remain volatile for a few months yet as the impacts of the previous lockdown work through and inevitably, Omicron hits," Zollner said.
"When the dust settles, we expect a slower pace of growth as consumers digest the new reality of higher interest rates, and the housing boom recedes.
"But that's not a bad thing - getting the economy back on a more sustainable path is important."