Alcohol and cars – a volatile mixAlcohol produces physiological effects on the human body that can turn safe drivers into potential killers.
Key text
Key textAccording to the most recent data available from the Australian Transport Safety Bureau, alcohol was implicated in about one-third of all road deaths in 1996.What is it about alcohol that turns even good drivers into potential killers? And how can individuals manage this pervasive drug so that they don’t become a danger on the roads?
The absorption of alcohol
The alcohol in every kind of drink – beer, wine and spirits – is called ethanol. There are many other kinds of alcohol, but most are more toxic than ethanol and not fit for human consumption. Ethanol is a small but very active and volatile molecule. It dissolves readily in water and is quickly absorbed into the bloodstream. The key measure in determining the effect of ethanol on the body is its concentration in the blood. This is usually called the blood alcohol concentration (BAC) and is measured in grams of ethanol per 100 millilitres of blood. For example, men and women 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. The rate of absorption of ethanol into the bloodstream helps determine the effect the ethanol has – the higher the rate of absorption, the higher the BAC will reach before the body’s metabolising processes convert the ethanol into other substances. When you have an alcoholic drink, ethanol is absorbed in three different places: to a minor extent through the tissues of the mouth and throat, to a greater extent through the stomach wall, and to the greatest extent through the wall of the small intestine, which the ethanol enters through a sphincter at the bottom of the stomach. The small intestine absorbs alcohol much more quickly than do other tissues and organs. Thus, the rate at which material passes from the stomach to the small intestine – ‘gastric emptying’ – is a key factor in determining how quickly ethanol is taken up into the bloodstream. Metabolising of ethanol
Most of the body's metabolising of ethanol into other substances takes place in the liver, which is the major detoxifying organ in the body. The liver first converts the ethanol to acetaldehyde, then to acetic acid and finally to carbon dioxide and water. Some ethanol is also expelled from the lungs through the act of breathing. This is handy for police: breathalysers analyse the ethanol content of air exhaled from the lungs and convert it to BAC by way of a special formula.
Effects on the brain
Alcohol – ethanol – is a depressant, which means that it slows the activity of the central nervous system (Box 1: Ethanol and the brain), increasing the time taken to react, diminishing judgment and reducing motor control. The depressant effect of alcohol puzzles some people; after all, some of the expressions associated with drinking – like ‘happy hour’ and ‘high as a kite’ – as well as the antics of many intoxicated people, seem to contradict this idea. But the apparent stimulatory effects of alcohol can be explained in terms of its depressive effects. The brain contains inhibitory centres that ordinarily moderate a person’s behaviour. Ethanol depresses the activity of these centres, thereby removing some of the barriers to extroverted, loud and aggressive behaviour. This effect can be dangerous on the road. While under the influence of alcohol we may be more inclined to drive above the speed limit, take unnecessary risks or otherwise engage in acts of foolish bravado, especially in the presence of our peers. There are other depressant effects that influence our capacity to perform well on the road. Several studies have demonstrated that a BAC of 0.1 – twice the legal limit – results in a 300-400 per cent increase in body sway, due to the inhibition of the brain’s sensorimotor coordination function. In another study, a BAC of 0.065, only marginally above the legal limit, resulted in a 10-12 per cent reduction in measures of hand-eye coordination. And other studies suggest that a BAC of 0.05-0.l can decrease perceptive abilities to such an extent that reaction time is slowed by up to 20 per cent. The general conclusion of scientists is that impairment of the brain’s ability to process information, make decisions and carry them out is evident above a BAC of 0.05 and markedly affected above 0.1.
The net effect on driving
Competent driving requires a variety of different skills – an ability to physically operate the car, an ability to perform more than one task at a time, an awareness of potential hazards, a capacity to react quickly to danger, and so on. Virtually all these skills diminish with increasing BAC. This is borne out by research suggesting that the risk of involvement in a motor vehicle crash in which one or more people are killed or require hospital treatment doubles with a BAC of 0.05 and increases more than four-fold with a BAC of 0.12.
How much can I drink and still drive?
In all Australian States and Territories, you commit an offence if you drive while your BAC is 0.05 or above. The legal limit is lower for certain road user groups (eg, those who hold learner or provisional licences). Depending on the State or Territory, this lower limit is either zero or 0.02. How does this translate into a ‘safe’ number of drinks? For those who must stay under 0.02, that’s easy – you can’t drive a car or ride a motorbike after even a single drink. For those permitted to drive with a BAC less than 0.05, it gets a bit more complicated. Your BAC at any given time is determined by a number of factors, including:
There are other factors: for example, drinks with a lot of fizz – such as champagne – are absorbed into the bloodstream more quickly than, say, wine. This is because the fizz irritates the stomach’s sphincter, which opens to allow the liquid into the small intestine where the rate of absorption is much higher. (The expression ‘champagne goes straight to my head’ is only partially incorrect. In fact, it goes straight to the lower intestine, from where it goes straight to your head.) This all means that calculating your BAC, and therefore your fitness to drive, is difficult. Nevertheless, various agencies have come up with approaches that give good rules of thumb for deciding how many drinks you can safely drink over a given time and how long you should wait after drinking before driving. You can also make use of breath-testers, which are coin-operated machines available in many pubs and clubs. You can even do an experiment: drink about as much as you normally would and then monitor your BAC as it rises, peaks and slowly declines. How long do you need to wait before it is safe to drive? Conducting the experiment on different occasions or with different beverages will show how different factors affect results. Plan ahead
By planning ahead you can avoid having to calculate your BAC at all. For example, when you go out with a group of friends, choose a 'designated driver'. The designated driver does not consume any alcohol. Or leave your car at home and use public transport or taxis.
Clear thinking?
The chances of becoming a crash victim increase dramatically when a driver is under the influence of alcohol, so it makes sense to avoid situations where you drink and then drive. But here’s a catch-22: once you start drinking, your ability to think clearly and act wisely diminishes. Recognising this while sober could be the first step towards safeguarding your own life, and the lives of others. Related Nova topics: Death-defying designs for car safety Fatal impact – the physics of speeding cars A fair cop! Accurate breath analysis and speed detection Bitumen battles – the phenomenon of road rage The shocking truth about road trauma Driver fatigue – an accident waiting to happen The dope on drug-impaired driving
Different neurotransmitters have different effects on the transmission of nerve impulses. Some promote this transmission while others inhibit it. Scientists have so far found hundreds of neurotransmitters, and the list is still growing. Ethanol appears to affect various neurotransmitters. One of these is glutamate, the major promoter of nerve impulses in the brain. Scientists believe that one of the main effects of ethanol on nerve ‘firing’ is a decrease in the activity of glutamate neurotransmitters, leading to a slowing down of brain activity. In addition, ethanol might increase the activity of another important neurotransmitter, gamma-aminobutyric acid (GABA). GABA’s role is quite different from that of glutamate in that it inhibits neuronal activity. When ethanol molecules bind to GABA receptors, the ethanol further inhibits neuronal activity. The parts of the brain that have GABA receptors include those responsible for movement, memory, and judgment.
Long-term effects of ethanol
Studies into the effects of ethanol on the brain are also increasing our understanding of longer-term problems, such as alcoholism and the effects of alcohol on health. These might be quite different from the short-term effects. For example, animals subject to long-term exposure to ethanol have been shown to have a reduced number of GABA receptor sites. As a result, the synapses of such animals are less effective in inhibiting nervous reactions such as seizures - perhaps explaining why chronic alcohol users experience more seizures than the rest of the population. Related sites
Related Nova topic:
Australasian Science June 2007, page 7 Alcohol cravings blocked Explores a part of the brain that blocks cravings for alcohol and other drugs.
September 2006, page 8 Just one drink can be dangerous Warns that drinking alcohol increases the chance of all types of injury.
April 2006, pages 30-32 Thinking about drinking: The power of expectation (by Sitharthan Thiagarajan) Looks at alcohol-related expectations of drinkers.
July 2004, pages 29-31 Insights from a drunken worm (by Andrew Davies) Explains how inebriated worms provide insights into the biological effects of alcohol.
New Scientist 5 September 2006 'Nano-flowers' show promise for alcohol detection (by Tom Simonite) Describes a sensitive nanocrystal for breath alcohol analysis and other applications.
4 April 2006 Drink-driver arm scanner (by Barry Fox) Describes an invention to do roadside blood alcohol tests, without taking any blood.
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.
30 July 2005, page 44-45 Zero tolerance for road slaughter (by Pelle Neroth) An interview with the director of Sweden's director of traffic safety about steps taken to decrease the road toll in Sweden.
21 August 2004, page 28-33 Intemperate society (by Alison Motluk) Looks at binge drinking and changing attitudes to drinking habits.
14 February 2004, page 14 Booze tests tell all about our drinking (by Andy Coghlan) A report on tests that reveal alcohol use in past days, weeks and months.
7 November 2002 Alcohol's erroneous ways revealed (by Emma Young) Reports on research indicating that two glasses of wine can change the brain’s ability to detect and correct errors.
20 March 2002 Drink-drive detector radios police (by Jonathan Beard) Describes a breath detector that is fitted to cars.
11 March 2002 Car computer could detect drunken steering (by Will Knight) Describes a computer designed to detect driver’s eye movement and steering.
Scientific American 5 April 2006 Staying sober (by Andreas Heinz) Covers recent research on brain chemistry related to alcohol dependency.
12 April 2004
From this page you can access information on drink driving topics.
Australian Drug Foundation
Federal Office of Road Safety Tables and graphs relating to road safety in Australia.
Trends in alcohol-related road injury in Australia, 1990-1997 (National Drug Research Institute, Curtin University of Technology, Australia)
Provides data on road related injuries categorised by the year, sex, age and state.
Coffee and alcohol (Great Moments in Science, Australian Broadcasting Corporation)
Looks at the myth that coffee can help you become sober when drunk.
How Stuff Works (USA)
Road Ready (ACT Department of Urban Services, Australia)
Provides information and activities for new drivers and their teachers.
neurotransmitter. A chemical substance, given off by the terminals of a nerve cell or nerve fibre, which affects the next nerve cell or fibre in the chain, thus allowing a message to be passed between different links in the chain. It is the arrival of the electrical impulse at the end of the nerve fibre that causes the release of a neurotransmitter into the small gap (called the synapse) between nerve cells. The neurotransmitter travels across the synapse and excites or inhibits the next nerve cell in the chain. sphincter. A ring of muscle surrounding a tubular organ or the opening to a hollow organ such as the stomach. When a sphincter muscle contracts, the organ is closed off. volatile. Volatile substances readily change from a solid or liquid form to a gaseous form. They have a low boiling point and a high vapour pressure.
External sites are not endorsed by the Australian Academy of Science. Posted December 1999. The Australian Foundation for Science is also a supporter of Nova.
This topic is sponsored by NRMA – ACT Road Safety Trust.
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