Impairment due to alcohol and/or drugs is a major cause of motor vehicle crashes worldwide. Alcohol, drugs and various medicines impair several of the driver's functional capabilities, and this leads to increased crash risk.
The crash risk for drivers with a blood alcohol concentration (BAC) of 0.5 g/L is estimated to be about 1.4 times higher than that of a sober driver; at 1.0 g/L, the risk is nearly 5 times higher; and at 1.5 g/L around 20 times higher. Looking at fatal crash data, the risk curve is even steeper, with the risk estimated to be almost twice as high with a BAC of 0.3 g/L, five times as high with a BAC of 0,5 g/L, and ten times as high at 0.8 g/L. The crash risk associated with illegal drugs or medicines depends on the type of drug or medicine. The greatest risk increase for illegal drugs - at least 5 times higher - was found for amphetamines, multiple drug use, and combined alcohol-drugs use. For medicines, significant risk increases were found for driving under the influence of barbiturates (used for treating headaches, insomnia, and seizures), benzodiazepines (used to relieve anxiety and insomnia), anti-depressants (used to alleviate depression), and opiates (used to treat pain or sleeping problems). The mechanisms through which drugs and medicines affect the body, the extent to which they impair driving, and the time taken for driving to be impaired differ greatly among drugs and medicines.
It has been estimated that 1.5 to 2% of kilometres travelled in the EU are driven by persons with an illegal BAC, while around 25% of all road deaths in the EU are alcohol-related. There is no reliable estimate of how many traffic crashes in Europe are drug-related. In a survey in European countries, asking about their driving in the previous 30 days, 21% of drivers admitted to have driven after drinking alcohol, 13% to have driven while they may have been over the legal alcohol limit, 15% to have driven after taking medicines that may affect driving ability, and 5% to have driven within 1 hour after taking drugs other than medication.
The reasons people drive while impaired reflect the opportunities that society provides for this, as well as individual motivation. In regard to the repeat offenders group, medical (psychiatric) problems related to problematic alcohol and drugs use often underly their habitual pattern of impaired driving.
Countermeasures against impaired driving include:
- General policies to decrease the consumption of alcohol and drugs
- Policies to reduce drink and drug use before intended driving
- Strict legislation combined with active police enforcement
- Provision of alternative means of transport
- Awareness campaigns, rehabilitation courses, and safety culture in companies
- Alcohol interlocks (breathalyser linked to ignition lock)
- In-vehicle technology that warns/intervenes when impairment leads to critical events.
At EU level, in 2001 the European Commission recommended legal blood alcohol limits of maximum 0.5 g/L with a lower limit of 0.2 g/L for novice and professional drivers. In 2022 (new vehicle types) and 2024 (all new vehicles) alcohol interlock installation facilitation will be mandatory for cars, vans, trucks, and buses.