The legal environment
In order to establish legislative limits for DUI, information on drug or alcohol intake and the effects on impairment must be available. Alcohol, the most widely abused drug, is the best understood in terms of use-related impairment. Numerous studies have been carried out measuring alcohol consumption, levels in the body and associated psychomotor performance (Moskowitz and Robinson 1988; Moskowitz and Fiorentino 2000). These studies indicate that alcohol consumption does result in impairment. Most jurisdictions have adopted limits on the level of alcohol which is considered accept able/unacceptable for an individual to have in their system while operating a motor vehicle. The limits differ greatly between jurisdictions. Norway and Sweden have adopted a ‘zero tolerance’ policy, that is persons should not drive after consumption of alcohol. However, to allow for analytical inaccuracy in measuring levels of alcohol and to account for ingestion of ethanol from alcohol-containing food and medicines, they have set a standard of 0.2 g/L, i.e. 0.2 g alcohol per litre of blood (a concentration roughly equivalent to that achieved by the consumption of one alcoholic drink in a 67.5 kg male over 1 hour), as the blood alcohol concentration above which all individuals are assumed to be impaired. In the rest of Europe, Australia and North America, the legislated BAC limits generally vary between 0.5 and 1.0 g/L; 0.5 g/L is permitted in Australia and much of Europe (Belgium, Denmark, Finland, France, Germany, Greece, Italy, The Netherlands), and 0.8 g/L in the United Kingdom and in most of North America (but with 1.0 g/L permitted in some states in the USA). The limit in Japan is 0.3 g/L. Some jurisdictions set alternative lower limits for younger (presumably less experienced) drivers, or drivers of commercial vehicles (i.e. buses and large trucks). Most jurisdictions also have an alternative offence of driving while affected by the consumption of alcohol ‘to the slightest degree’, or some such similar language, to allow prosecution of individuals intoxicated by BACs below the statutory threshold. Some jurisdictions also have BAC levels above which more serious charges may be brought.
As noted above, alcohol is known to diffuse from the blood into the lungs and can be eliminated via breath. The relationship between levels in blood and breath has been established, the reby permitting the introduction of breath alcohol testing; legislative limits for breath alcohol have been introduced in many jurisdictions. Legislating against driving under the influence of drugs presents a greater difficulty since there is less information available about how drugs impair driving, or how impairment can be associated with a quantitative measure of the drug in a person’s system. It is relatively simple to carry out studies on alcohol intake and impairment because alcohol is legal in most countries and hence can be administered for studies without raising undue ethical considerations. This is not the case with many drugs, particularly those such as cocaine, opiates and amfetamines which are generally regarded as prohibited substances in most countries. Deliberately administering these substances to test impairment raises considerable ethical issues, particularly at concentrations simulating recreational use. Even for the studies which have been carried out, there seems to be no simple correlation between blood concentrations of the drug and effects on impairment. Thus, unlike for alcohol, in many jurisdictions there are no readily accepted values for drug concentrations in body fluids at or above which it is assumed a person’s driving will be impaired. Consequently, many jurisdictions have introduced impairment tests for individuals suspected of drug impaired driving. These are typically tests of co-ordination skills but may also include observation of physical parameters such as pupil size. Although such tests may indicate impairment, for prosecution purposes the link to impairment through drug intake must be made. This is demonstrated generally through a chemical test of blood or urine, and more recently of oral fluid. The relative merits of these sample types is discussed later. Where the law is set so that no actual concentration limit is set for the offence, a toxicologist is generally relied upon to provide the necessary link between the use of that drug, the significance of any of the quantitative results and the drug’s potential effects on psychomotor skills, particularly those related to driving. Some jurisdictions have adopted quantitative ‘per se’ limits for drugs in blood or urine above which the person’s driving is assumed impaired. These laws are generally based on the principle that the use of some drugs is illegal, or that they are used principally for recreational purposes and not necessarily on whether there is a demonstrated link between the limit set and impairment. The pharmacological merits and limitations of this approach are made evident in a later section.
