Another barometer of the economy is showing signs of declining activity, with volumes of trucks and cars on our roads falling in September.

ANZ's TruckOmeter measures the volumes of traffic on key roads across New Zealand, as a guide to future activity.

The bank said today that its heavy track index, which measures vehicles weighing more than 3.5 tonnes on 11 roads, fell a seasonally adjusted 5.3 per cent in September. The fall undid gains in the previous month, and is now at the lowest level since July 11.

Senior economist Sharon Zollner said the result "suggests the relatively strong growth seen in the first half of 2012 is unlikely to be sustained in [the September quarter], for which it is predicting slightly negative growth in gross domestic product".

Meanwhile the light traffic index, which measures mainly cars on nine roads across New Zealand, claims to give a six-month lead on likely future growth, although ANZ places less faith in it than the heavy index.

However, the message was similar to the heavy index, and gloomy. Light traffic fell 2.1 per cent in September, unwinding the August gains, suggesting growth will remain weak into the start of 2013.

"Both indexes suggest the pace of annual economic growth is set to ease from its current 2.5 per cent pace," Zollner said.

"Given the clear signs of slowing in our two largest trading partners, China and Australia, an exchange rate that appears stuck over US80c, and an ongoing need to unwind previous excesses and repay debt, this would be entirely understandable," Zollner said.

"However, traffic data can not be expected to pick up the Christchurch rebuild. This may prove to be a well-timed stimulus."

- © Fairfax NZ News