The dope on drug-impaired driving
Key text
This topic is sponsored by NRMA – ACT Road Safety Trust.
Since the 1990s the prevalence of drug-impaired driving in Australia has increased and this has not gone unnoticed by police and politicians.
The Victorian Parliament recently gave motorists something to chew on. In December 2003 it passed legislation empowering police to randomly test drivers for the presence of the active component of cannabis (tetrahydrocannabinol or THC) and methamphetamines (also known as speed, ice and crystal meth). Drivers’ saliva will be tested using an absorbent collector. To collect saliva drivers will be asked to touch their tongues to the collector, place it in their mouths or chew on it. Anyone found guilty of driving with these illicit drugs in their bodies faces fines of up to $1200 and a possible cancellation of their driver’s licence.
Victoria started testing drivers in December 2004, and other Australian states are contemplating similar measures in their efforts to reduce the problem of drug-impaired driving (drug-driving) because it is fast becoming a major road-safety problem.
What is drug-driving?
One way of defining drug-driving is the driving of a motor vehicle while under the influence of drugs other than alcohol (while alcohol is technically a drug, drink-driving is usually treated as a separate issue). Another is the driving of a motor vehicle with the presence of drugs other than alcohol in the system. These two definitions might look pretty much the same but, as we will see, the difference between them is important when it comes to designing legislation.
Drugs of particular concern to road-safety authorities are those that could impact driver performance. They include depressants such as cannabis, methadone and heroin, stimulants such as speed, cocaine and ecstasy, and hallucinogens such as LSD.
Some prescription drugs can also affect driving; tranquillising drugs such as rohypnol and oxazepam, for example, can make users drowsy and almost certainly more liable to err while driving. However, the Victorian drug-driving legislation does not make it an offence to drive while using such drugs.
The increasing threat of drug-driving
Drug-driving appears to be quite prevalent in Australia. A 2003 survey of 19–23-year-olds in Victoria found that more than half had used such drugs in their lifetime, while 28 per cent of surveyed males and 17 per cent of females admitted to driving a motor vehicle while under the influence of an illicit drug. Another survey in Western Australia in 2001 estimated that 17 per cent of drivers aged 20–29 years had driven a vehicle while under the influence of drugs. A third survey, this time of injecting drug-users in Sydney, revealed that 88 per cent of those users who had driven a vehicle in the previous 12 months had drug-driven in that period. About 4 per cent of respondents (6 per cent of men and 2 per cent of women) to the 2001 National Drug Strategy Household Survey admitted that they had driven while under the influence of drugs in the previous 12 months.
Perhaps the most worrying study of all was carried out by researchers at the Department of Forensic Medicine at Monash University. The study looked for the presence of drugs in 3398 drivers who died in crashes in New South Wales, Victoria and Western Australia in the period 1990-1999. It found that drugs (other than alcohol) were present in 26.7 per cent of all dead drivers. The study also found that the prevalence of drugs increased over the decade.
How drugs can affect driving
While such a finding doesn’t prove a direct relationship between drug use and road deaths, it serves to alert legislators to the problem. But they faced some significant practical problems in designing laws to limit drug-driving. The intensity and nature of a person’s reaction to a drug depends on several factors, and therefore deciding on a threshold amount – over which driving might be considered to be impaired – is very difficult. A person’s reaction to drugs is influenced, for instance, by past exposure to the drug and by genetic differences, as well as by the ‘quality’ of the drug, which for illicit drugs is highly variable. Further complicating things is the common practice of using more than one drug (including alcohol) simultaneously. These factors and others make predicting the effects of drugs on driving an inexact science.
Nevertheless, some general observations can be made. Depressant drugs tend to slow reactions and reduce concentration. Experiments have shown that users of cannabis find it difficult to stay in one lane on the road and may be unaware that they are drifting into the path of oncoming traffic. Drivers under the influence of cannabis may also find complex driving situations, such as busy roads or uncontrolled intersections, more difficult to negotiate than they would when driving drug-free. Stimulants like speed might make drivers over-confident and aggressive, while those under the influence of hallucinogens like LSD might react erratically to imaginary obstacles or sounds.
Testing for impairment
Two basic approaches can be taken to detect drug-drivers: testing for the impairment of driving performance; and testing for the presence of drugs.
The impairment approach, which takes as a starting point our first definition of drug-driving, involves the use of tests like the Standardised Field Sobriety Test (Box 1: Standardised Field Sobriety Test), in which drivers are required to perform tasks designed to test the extent to which they are intoxicated by alcohol. This test has been adapted to measure the extent to which a driver’s use of drugs might hinder performance equivalent to certain levels of blood alcohol content (BAC). The Standardised Field Sobriety Test and other similar impairment tests, including the more refined ‘drug evaluation and classification’ program, have been shown to measure the degree of drug-induced impairment at quite a high level of reliability, although they are far from foolproof.
In most Australian states, police use what might be termed a ‘driving under the influence’ approach, in which they are able to arrest a driver they suspect of driving under the influence of a drug to the extent that driving performance is impaired. The suspect may be required first to take an impairment test and then to provide a blood or urine sample, which is tested for the presence of various drugs.
Presence of drugs
The limitation of the driving-under-the-influence approach is that it is only implemented when police have cause to suspect a driver and doesn’t act as a strong deterrent to drug-driving. An option for overcoming this is random testing, in which drivers are pulled over arbitrarily for drug-testing, just as is done for alcohol.
Testing for drugs at the roadside, however, is not as simple as it is for alcohol. For a start, the range of drugs that could impair driving is wide, although their actual impacts on safety are often not well known. Moreover, few drugs are detectable in the breath like alcohol. A sample of bodily fluid may therefore be needed, but collecting such fluid – particularly blood and urine – can be a messy and invasive process. For this reason, biochemists have spent a great deal of time and energy on developing tests using bodily fluids that are more easily collected, such as saliva or sweat.
There’s another difference between random drug-testing and random alcohol testing. The relationship between BAC and the risk of crashing is well known; the BAC threshold, which is set at 0.05 per cent in Australia, is a well-accepted standard. Setting thresholds for other drugs is more difficult: the study of the relationship between most drugs and driving is still relatively new and little is known about the relationship between drug use and crash risk.
In Victoria’s planned introduction of random drug-testing, drivers will be stopped at random and asked to submit a saliva sample. This will be placed in a device that uses a process known as immunoassay to test for the presence of specific drugs.
Drivers who return a positive result from the first saliva test will be required to provide a second sample; if that is also positive they will be interviewed by police and allowed to leave (but not to drive). The saliva sample will be sent to a laboratory for more accurate testing, which may take some days; if this confirms the presence of an illicit drug, the driver may be prosecuted.
Impairment or presence?
Critics argue that the link between the ‘presence’ approach and road safety is tenuous, since the detection of an illicit drug in a person’s saliva does not indicate whether that person is fit to drive or not. Civil libertarians suggest that the approach constitutes a significant breach of privacy for what may be a negligible effect on road safety. But advocates say that the real power of random testing is in the message it sends: drug-driving is dangerous, and it’s about time drivers were up to speed with that.
Box
1. The Standardised Field Sobriety Test (SFST)
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The shocking truth about road trauma
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to happen
Page updated February 2006.