The effects of alcohol and psychotropic drugs on motor driving (Fig. 10.3) have been the subject of well-deserved attention, and many countries have made laws designed to prevent motor accidents caused by alcohol. The problem has nowhere been solved. In general it can be said that the weight of evidence points to a steady deterioration of driving skill and an increased liability to accidents beginning with the entry of alcohol into the blood and steadily increasing with blood concentration.
Alcohol plays a huge part in causing motor accidents, being a factor in as many as 50%. For this reason, the compulsory use of a roadside breath test is acknowledged to be in the public interest. In the UK a blood concentration exceeding 80 mg alcohol/ 100 ml blood (17.4 mmol/1)28 whilst in charge of a car is a statutory offence. At this concentration, the liability to accident is about twice normal. Other countries set lower limits, e.g. Nordic countries,29 some states of USA, Australia, Greece.
So clearly is it in the public interest that drunken driving be reduced that the privileges normally attaching to freedom of conscience as well as to personal eccentricity must take second place. In one instance, an ingenious driver, having provided a positive breath test, offered a blood sample on the condition it should be taken from his penis; the physician refused to take it; the police demanded a
28 Approximately equivalent to 35 micrograms alcohol in 100 ml expired air (or 107 mg in 100 ml urine). In practice, prosecutions are undertaken only when the concentration is significantly higher to avoid arguments about biological variability and instrumental error. Urine concentrations are little used since the urine is accumulated over time and does not provide the immediacy of blood and breath.
29 In 1990 Sweden lowered the limit to 20 mg/100 ml, which has been approached by ingestion of glucose which becomes fermented by gut flora—the 'autobrewery' syndrome.
urine sample; the subject refused on the ground that he had offered blood and that his offer had been refused. He was acquitted, but a Court has since decided that the choice of site for blood-taking is for the physician, not for the subject, and that such transparent attempts to evade justice should be treated as unreasonable refusal to supply a specimen under the law. The subject is then treated as though he had provided a specimen that was above the statutory limit. Yet another trick is to take a dose of spirits after the accident and before the police arrive. The police are told it was taken as a remedy for nervous shock. This is known is the 'hip-flask' defence.
Where blood or breath analysis is not immediately available after an accident it may be measured hours later and 'back calculated' to what it would have been at the time of the accident. It is usual to assume that the blood concentration falls at about 15 mg/100 ml/h. Naturally, the validity of such calculations leads to acrimonious disputes in the courts of law.
Ability to drive can be impaired by many prescribed drugs. In road traffic accident fatalities 7.4% of persons had taken a drug 'likely' to affect the CNS (chiefly older subjects). In addition, cannabis was found in 2.6%. Unfortunately, accurate control figures are not available except in the case of epilepsy: 1.3% of fatalities had taken an antiepileptic drug and the incidence of the disease in the general population is 0.4%.3C Driving may also be influenced by antihistamines (drowsiness, but less commonly with newer nonsedative agents), mydriatics and antimicrobials for topical ocular use (blurred vision), antihypertensives (hypotension) and insulins and oral antidiabetic agents (hypoglycaemia).
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