A former police crash analyst says police have been too quick to attribute the causes of fatal crashes at Labour Weekend.
Police say a major anti-speeding operation over the holiday long weekend was not a failure, even though eight people died on the roads - the same number as last year.
Police say it was a tragedy that so many lives were lost over the weekend.
National road policing manager Superintendent Paula Rose says while the toll is disappointing, because police wanted a fatality-free weekend, the policing operation targeted the right issues.
"The three themes that have come through from our eight deaths have been around speed, failing to keep left and alcohol. So yes, we do think we were right to focus our efforts in those areas."
But a former police crash analyst, Hamish Piercy, says police often attribute the cause of crashes too early - when it can take days to establish.
"When they have a low crash total like we had at Queen's Birthday, the police are the first ones to put their hand up and say it was all their efforts and then they potentially ignore other factors like the weather we experienced on that occasion.
"Yet when we have a weekend where we have a higher road toll, they're the first ones to say, 'Oh it's not our fault'. So it feels like at times the police are having it both ways."
Mr Piercy says more work needs to go into driver training and road engineering - not just enforcement.
The holiday weekend began on Friday at 4pm and ended at 6am on Tuesday.
Road toll disappointing - minister
Transport Minister Steven Joyce says road toll of eight deaths is disappointing.
He says there was a big effort by police at the weekend, but the road toll is dependent on the behaviour of individual motorists, and officers cannot be around every corner.