Drug use among drivers is almost as common among drivers as alcohol use, a survey suggests. (Eraldo Peres/Associated Press)Doug Beirness and Erin Beasley of the Canadian Centre on Substance Abuse in Ottawa published the results of a roadside survey on alcohol and drug use among drivers in British Columbia in the journal Traffic Injury Prevention.

Beirness presented the research at the International Council on Alcohol, Drugs and Traffic Safety in Oslo, in August 2010, then outlined his findings for CBCNews.ca.

Another Canadian study presented at the Oslo conference found that 33 per cent of more than 14,000 drivers killed in accidents nationwide tested positive for at least one drug and 38 per cent tested positive for alcohol. That study, of driver fatalities from 2000 to 2006, was also carried out by the Canadian Centre on Substance Abuse.

Beirness is calling for an impaired-driving awareness campaign that includes both alcohol and drugs.

Could you please specify what were the most common prescription drugs in the B.C. survey?

The toxicology results do not provide specific drug names — just types. For examples, opiates and amphetamines were among the most commonly found substances that can be prescribed as medications to treat specific ailments. However, it is impossible in a survey such as this to determine whether or not the person was taking the substance under the supervision of a physician. It is also not possible to determine if the person was using the medication properly.

Why is this research important?

The survey revealed that drug use is at least as common among drivers as alcohol use. This tells us that we need to be paying more attention to this issue. The research also shows us that patterns of drug driving appear to be different from patterns of alcohol and driving. For example, alcohol use among drivers is most common on weekend nights and increases later at night. Drug use is more evenly spread throughout times and days.

What is extent of the link between drug impairment and collisions? How does this comparing to driving impaired by alcohol or driving while using a cellphone?

Research on the risks associated with driving after specific drugs lags behind that on alcohol and driving. From existing studies, there is evidence that driving after drug use increases the risk of crash involvement. The risks are higher when drugs are combined with alcohol and when more than one substance is used.

Driving while using a cellphone is not comparable to driving after alcohol or drugs. Cellphone use is generally a "time-limited" distraction — it creates a risk while the person is using the phone. Drugs and alcohol create an impaired state that affect driving performance so long as the person is driving.

How many drivers in the roadside survey tested positive for both alcohol and drugs?

Overall, the use of both alcohol and drugs was relatively rare. However, among drivers who tested positive for drugs, 17% had also been drinking.

What were their blood alcohol concentrations?

From the study, about one in every six drug-positive drivers (16.8 per cent) also tested positive for alcohol. Just over half (52.0 per cent) had a BAC of at least 50 mg/dL; 23.8 per cent had a BAC in excess of 80 mg/dL.

How long could cannabis be in the driver's system and be detected compared with alcohol and drugs?

Alcohol is metabolized at a rate of about 15mg/100ml an hour. That means that a person with a BAC of 100 would not return to a 0 BAC for almost 7 hours. The metabolism of other drugs varies by drug. The metabolites of cannabis can be detected in blood and/or urine for several days or even weeks following use, depending on factors such as the extent of use and user history.

The active chemical in cannabis can generally only be detected in oral fluid samples for 90 to 120 minutes following use.