Researchers are on the roads trying to estimate how many people are driving around just under the limit in the face of the Government's refusal to lower drink-driving thresholds.
Canterbury University senior lecturer Eric Crampton was out with Christchurch police on Friday night looking for drivers who had been drinking.
Dr Crampton said it was impossible to know whether the number of people killed in crashes involving drivers with blood-alcohol readings of 50mg to 80mg was high until it was known how many drivers were on the road with that level of alcohol in their systems.
"There's a lot we don't know about what's going on.''
For instance, if a third of drivers were in that range and 30 per cent of the crash deaths were as well, that was about what would be expected.
Dr Crampton's outing was to check how many research assistants would be required to discover the number of drivers with levels of alcohol in their systems below the legal limit.
A record is kept of readings that exceed the limit, but there is no data retained on drivers with readings below the limit.
"It will take someone walking around behind the police,'' Dr Crampton said. If the study was feasible, he would try to get funding for it.
Economics and finance professor Glenn Boyle said until such a study was done, people might be drawing a link where there wasn't one.
He said the number of crashes involving alcohol readings between 50mg and 80mg needed to be put into the context of the total number of people on the road with those readings.
National Addiction Centre director Professor Doug Sellman is convinced there is a link
He said every time someone died in an alcohol-fuelled car crash, it was a chance to point out that former Transport Minister Stephen Joyce was partly responsible.
The Government has refused to move on a lower blood-alcohol limit for drivers until it receives the results of data from the Ministry of Transport and a driver-simulation study from Waikato University.
Prof Sellman said Government "delay tactics" were costing lives. All the information was already available to make a decision, he said.
"Joyce didn't act on the international research that was there already. None of the research says we need more research. Only Stephen Joyce believed that."
Prof Sellman said the point of a lower limit was that it would reduce the number of drivers with higher alcohol levels, too.
Statistics show 20 people had been killed in the past four years in road accidents involving drinking drivers who were just under the legal limit.