Drug-screening devices that could be used by police to catch impaired drivers at the roadside may be more likely to show drug-positive results in extreme cold, according to a new study by Public Safety Canada.

Between December 2016 and March 2017, police at seven detachments across Canada tested two saliva-screening devices — the Securetec DrugRead and the Alere DDS-2.

With the federal government having committed to legalizing marijuana by July 1, 2018, the pilot project goal was to test the reliability of the devices as tools for enforcement of drug-impaired drivers.

Sask. tests part of study

Police at the North Battleford RCMP detachment were among 53 officers who were trained to use the devices.

Although the final report on the project gives the devices an overall positive review, it also raises questions about their reliability in certain weather conditions.

The results showed they were proportionately more likely to show drug-positive results in extreme cold temperatures.

The cartridges used in both devices have a suggested operating range above freezing; the Securetec DrugRead's suggested temperature range is between 5 C and 25 C, while the suggested Alere cartridge range is between 15 C and 25 C.

While 64 per cent of all tests occurred outside the suggested temperature range, 80 per cent of all positive results were from tests taken outside the recommended range.

"At present, it is unknown whether this finding is attributable to technical or procedural issues, for example whether the devices are more likely to show positive results when tested in extreme cold temperature," said the report.

An Alere DDS-2 Mobile Test System like the one used in the pilot project. (CBC)

More research needed

It suggests more research is needed on the reliability of the devices in various weather conditions.

The report also recommends that additional measures be taken to keep devices and swabs at operating temperatures in areas with extreme weather conditions.

The samples were collected through random stops and roadblocks, with 80 per cent taken from drivers and 20 per cent from passengers.

Overall positive reviews

In about 90 per cent of the samples taken, police described the devices as "very easy" or "easy" to use.

The report says malfunctions occurred in about 13 per cent of the samples taken, and the majority of those related to the printer functions.

Overall, the report concluded that with the proper training and standard operating procedures, the devices would be a "useful additional tool for Canadian law enforcement to better detect individuals who drive under the influence of drugs."

In addition to the North Battleford RCMP, the project was also carried out by police in Vancouver, Halifax, Toronto, Gatineau and Yellowknife, and by the Ontario Provincial Police.