Drugs other than alcohol

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There are a number of drugs (both legal and illegal) that have the potential to increase the risk of road crashes including: cannabis benzodiazapines eg valium hallucinogens eg LSD antihistamines eg in hay-fever tablets amphetamines eg speed opiates eg heroin. Many of these drugs reduce driving-related performance in tests, simulations and in ‘off road’ and ‘on road’ studies. There are also concerns that some drugs, including amphetamines, can be linked with aggressive driving, and (when used to combat extreme tiredness) with the risk of sudden onset of sleep.

However, despite the widespread use of cannabis and impressions given by some drug-driving reports, evidence suggests that alcohol is a bigger road safety problem than all other drugs combined.

Drugs and crashes
An Austroads report published in 2000 estimated that:

• If no drivers used alcohol, the number of fatal crashes would be reduced by about 25% and serious injury crashes by about 9%.
• If use of all other drugs by drivers could be eliminated, the number of fatal crashes would be reduced by up to 11% and serious injury crashes by about 1%.

Other findings
The total number of drivers involved in crashes who are detected as having used alcohol or other drugs are higher than those above as, even if alcohol or drugs have been used, they are not always the cause of the crash.

Drugs are more likely to be detected in the blood of fatally injured drivers than in the blood of less severely injured drivers. The story is much the same for alcohol, where fatally injured drivers are much more likely to have alcohol in their blood than are less severely injured drivers.

More recent data
Application of the Austroads (2000) analysis to more recent data gives an estimated:

• 24% fatal crash reduction if no drivers used alcohol
• 13% if no drivers used other drugs.

Cannabis
Cannabis is the drug most commonly detected in fatally injured drivers and riders in Australia. Research found that the odds of involvement as the driver at fault in a fatal crash were:

• 2.7 times higher for those using cannabis only, compared to those of drug and alcohol free drivers
• 6.6 times higher for drivers and riders with the highest levels of cannabis
• 6.0 times higher for drivers and riders with a Blood Alcohol Concentration (BAC) over 0.05.

Drug-driving reports
There are reports of drugs other than alcohol being detected in a substantial proportion of Australian drivers involved in crashes eg in 31% of Victorian driver fatalities.

But these may give a false impression as they often include drivers:

• using alcohol as well as the other drugs eg currently about 4 in 10 of Australian drug-positive drivers also have a BAC over 0.05
• who have traces of drugs in their blood, but who are not necessarily drug-impaired at the time of the crash eg traces of cannabis can often be detected some days after use
• using drugs at low levels that might not increase crash risk.

Other important information
The Austroads (2000) report on Drugs and Driving in Australia can be found at the Austroads Web site, by following the links to “Publications”. The report number is: AP-R172/00