The Automobile Association says research needs to be done to understand why the road toll is down so much this year.
In the first six months of the year, 139 people died on the roads - more than 50 fewer than the previous half-year low.
The Government says factors such as higher petrol prices, ongoing safety improvements and legislative changes are contributing to the falling toll.
But the AA says in-depth research analysis is needed to understand why the drop is happening.
However, Transport Minister Steven Joyce says it's a little early to get into research mode.