A jump in ANZ's Truckometer indicator is a good sign for the economy, but more likely about the current quarter than later in the year.

The Truckometer is based on traffic flows on carefully selected roads which have provided a good pointer to economic activity, measured by gross domestic product, six months later.

It jumped 3.3 per cent last month on a seasonally adjusted basis, reflecting a 2.7 per cent increase in light traffic, mainly cars, and a 7.5 per cent increase in heavy traffic.

ANZ economist Sharon Zollner, who devised the Truckometer, said if it simply reflected people taking delayed weekend trips in May's warm weather, then the implications for GDP were limited. "But if it's real production, then it should not be discounted."


Much of the increase in heavy traffic was on major routes to and from dairy factories, she said.

Autumn dairy production is estimated to be at least 35 per cent higher than its four-year average.

"We therefore suspect that, while some of the large jump may well be noise, much of it is a real economic signal, but one that refers to the June quarter rather than the December quarter, as the Truckometer's lead would usually imply."

If so, it is a timely boost.

"The light traffic was suggesting that the base momentum [in the current quarter] was going to be fairly weak so it is pretty nice timing to have an offset from primary production."