The dope on drug-impaired drivingThis 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. Key text Key textThe 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. Alcohol and cars – a volatile mix The shocking truth about road trauma Driver fatigue – an accident waiting to happen
Box 1. The Standardised Field Sobriety Test (SFST)The first of three tasks conducted under the SFST is the ‘horizontal gaze nystagmus test’. The police officer asks the driver to look at an object (such as a torch, pencil or finger) held about 30 centimetres in front of the driver’s eyes above eye-level. Drivers are then asked to track the object with their eyes as it is moved slowly to the side. This test is designed to evaluate the degree to which the driver is suffering from nystagmus – the involuntary jerking of the eye that occurs when the eyes look to the side – which commonly occurs at a smaller angle from straight ahead under the influence of alcohol. For each eye the officer looks for three clues including a lack of ‘smooth pursuit’ (jerkiness in the eye as it follows the object) and the onset of nystagmus prior to 45 degrees. The second task is the ‘walk-and-turn’, which itself comprises two parts. In the first part, the driver must stand heel-to-toe while the police officer explains the test. In the second part, he or she must take nine heel-to-toe steps in a straight line, turn around and repeat the steps in the opposite direction. Officers are trained to score the performance against eight clues, including an inability to follow instructions, over-balancing and taking an incorrect number of steps. Drivers who score two or more clues are classified as having a BAC, or drug-induced BAC equivalent, of over 0.01 per cent. In the third task, the ‘one leg stand’, drivers are asked
to stand with their arms at their sides and to hold one leg at least 15
centimetres above the ground for 30 seconds, counting out the number of
seconds as they do so. Officers look for four clues including swaying
and putting the foot down. Related sites
Activities
Further reading
Australasian Science May 2002, page 11 Tranquillisers a driving menace (by Stephen Luntz) Describes research from the University of Adelaide that found a link between tranquilliser use and road accidents. The Helix February/March 2002, pages 10-15 Drugs – science behind the substance (by Roger Beckmann) Looks at the chemistry behind how things we eat or drink can change our thoughts, feelings and behaviour. New Scientist 3 December 2005, pages 28-29 Taking on the drugged and drunk drivers (by Paul Marks) Describes technology to test drivers for the presence of drugs in their bloodstream.
2 December 2005 Cannabis doubles the risk of fatal crashes (by Gaia Vince) Describes research indicating that cannabis almost doubles the risk of fatal car crashes.
7 February 2005 Marijuana makes blood rush to the head (by Katharine Davis) Looks at the effect of smoking marijuana on blood flow in the brain.
13 November 2004, pages 32-39 The intoxication instinct (by Helen Phillips and Graham Lawton) Looks at the universal pursuit of intoxication by humans.
22 November 2003, page 25 End of the breathalyser? (by Graham Lawton) A report on a new kind of test used to determine if drivers are fit to be behind the wheel.
23 March 2002, page 4 Dope at the wheel (by Arran Frood) Looks at the question of having a legal limit for cannabis.
16 December 2000, page 6 Don’t be a dope (by Arran Frood) Describes research that found that cannabis adversely affected driving ability, although not as much as alcohol.
Useful sitesDrug driving and road crashes – an overview (ACT Department of Territory and Municipal Services)
This paper discusses a range of issues related to road crashes and drug driving. It reviews data on the extent of drug use among drivers, drugs of concern for their potential to impair driving ability and the actions taken by at the territorial, state and federal level in Australia to address the issue.
Australian Drug Foundation
Road to recovery: Report on the inquiry into substance abuse in Australian communities (House of Representatives Standing Committee on Family and Community Affairs, Australia)
This wide-ranging report on drug use was tabled in 2003. Chapter nine reports on the contribution of substance abuse to road trauma in Australia; the role of government in regulating road use and safety; and the prevalence and risks associated with drug driving. It includes recommendations for possible approaches to reduce the incidence of drug driving.
The incidence of drugs in drivers killed in Australian road traffic crashes (Forensic Science International, 8 July 2003)
Research article that reports on the incidence of alcohol and drugs in fatally injured drivers in Victoria, New South Wales and Western Australia for the period of 1990-1999. Reference list contains many links to other studies into drug driving.
Even some prescription drugs don’t mix with driving (Wellness Center, Cascade Health Solutions, USA)
Describes some effects of prescription, over-the-counter and illegal drugs on driving. Includes relevant links to other sites.
Australian Broadcasting Corporation
Drugs and driving (Office of Road Safety, Western Australia)
Looks at how and why drugs affect driving. Aimed at 14 to 24 year olds.
Saliva as an analytical tool in toxicology (International Journal of Drug Testing, Florida State University, USA)
This lengthy review article covers the anatomy and physiology of the salivary gland, saliva formation, how drugs transfer from blood to saliva and the techniques and methods for the measurement of drugs in saliva.
The effects of drugs on the nervous system (University of Washington, USA)
Includes information on a large number of drugs including cannabis, amphetamines, rohypnol, cocaine and LSD.
Glossaryblood alcohol content (BAC). The concentration of ethanol in the blood, which is a key measure in determining the effect of ethanol on the body. It is measured in grams of ethanol per 100 millilitres of blood. For example, people with a BAC of 0.05 grams per 100 millilitres – the legal limit for most drivers – have 0.05 grams of alcohol in their body for every 100 millilitres of their blood. depressant. A substance that slows down the functions of the central nervous system. More information can be found at About drugs (Australian Drug Foundation). hallucinogen. A substance that alters perception and can induce delusions or hallucinations. More information can be found at Hallucinogens (New South Wales Department of Health, Australia). immunoassay. A laboratory test that uses antibodies to identify and quantify substances. Often the antibody is linked to a marker such as a fluorescent molecule, a radioactive molecule, or an enzyme. stimulant. A substance that speed up the functions of the central nervous system. For more information see Stimulants (Missouri Department of Mental Health, USA). External sites are not endorsed by the Australian Academy of Science. The Australian Foundation for Science is a supporter of Nova. This topic is sponsored by NRMA – ACT Road Safety Trust. |