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Alcohol
Cannabis
Stimulants
Prescribed Drugs
The
Inexperienced Driver
Publications
Why worry about alcohol and driving?
Road trauma is the commonest cause of premature death amongst young adults in Australia. Transport safety continues to be improved by better engineering of roads and vehicles, but the the human factor remains.
Transport mishaps are not new. In the pre-industrial a good horse with an incompetent, intoxicated driver could share the responsibility for safe transport, and plod homeward in relative safety. The advent of the horseless carriage brought the era of such forgiving transportation to an end. The consequences of combining alcohol and transportation became more serious.
Who has crashes?
Epidemiology of vehicular accidents
One way of studying the drinking driver is to study the people apprehended for driving offences. Such surveys cannot provide information about the general population because they are, by definition, studies of that selected subgroup who have been detected by the police. They may not be typical of the general community. Excluding "random breath testing", police officers do not usually apprehend drivers randomly, nor are police randomly distributed in time or place: police patrol known "trouble spots" and interact with those individuals who come to notice because of their driving style, vehicle or other attributes. All that can be concluded from these studies are the characteristics of those drivers chosen by police for arrest or breath analysis. The results reflect the behaviour of police as much as driver characteristics.
Post accident surveys studies are similar to the post-arrest studies: these drivers are selected by involvement in a collision. Many such studies are simply demographic descriptions of the drivers with little attention being paid to the interaction of the many variables. Several studies have looked at patients presenting to hospital accident and emergency departments for non-accident related reasons. One study of 246 patients admitted to a casualty ward over a 6 week period showed 31% (55) to have blood alcohol concentrations over 0.05%, and 8.5% of the sample were over 0.15% (21 subjects). There was no sex difference in the numbers with positive blood alcohol concentrations but the males had higher levels than the corresponding females. Most positive blood alcohol concentrations were noted between 6 p.m. and 3 a.m. and the greatest proportion were at the weekend. A study of 208 patients admitted to Melbourne teaching hospitals in 1974 as a result of road trauma showed a similar distribution with 31% over 0.05% and 7% over 0.15%.
Population studies: several large studies have attempted to determine the relationship between alcohol and crash involvement. See table.
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Relative risk of accident |
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Single-vehicle crashes provide the only true measure of the contribution of alcohol to increasing the rate of crash involvement because non-impaired drivers may be able to compensate for the impairment of others. If one examines the probability of fatal single-vehicle crashes involving alcohol then if the BAC is 0.02-0.04% fatal crash involvement increases by 40 percent; between 0.05 and 0.09 % fatal crashes increase by 1,100 per cent; between 0.10 and 0.14% the probability goes up by 4,800 percent; and at levels >0.15% the risk increases by 38,000 percent.
Driving skill
Driving skills have been studied in driving simulators, in on-the-road situations and as a cause of epidemic disease.
Driving Simulators have been used as experimental models of real driving because of their inherent safety advantage over on-the-road testing. The more complex the test challenge given, the lower the BAC at which error rates are observed. Steering errors are noticed at BACs of 0.03% and collision frequencies increase; subjects tend to ignore rules and instructions at BACs about 0.05%. At these low levels subjects are more sluggish to correct positional errors. Drinking experience does not make any difference to driving ability at levels over 0.06%.
Closed driving course assessments are used as a more lifelike model of road?driving tasks. The more complex the task required the greater the deficit produced by alcohol. Increasing blood alcohol levels result in progressive impairment of driving performance clearly demonstrated in noncompetitive drivers at 0.05% and in competition drivers at 0.08%. The alcohol impaired driver may use past experience and learning to cope with normal routine driving demands, but fails to adapt as well in an "emergency" situations.
On-road Driving is rarely used in intoxication research for ethical and legal reasons. The only reported studies are from Holland and show that drivers with BACs in the range 0.034 to 0.051% were significantly impaired with no subjective awareness that their driving was in any way affected.
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