A blood alcohol level of 0.5 g/l increases the risk of an accident two-fold. Above 0.8 g/l the risk is multiplied by 10. Overall, alcohol is implicated in less than 10% of non-serious accidents, in 25% of accidents causing injury to the driver and/or passengers, in 50% of fatal collisions and in 65% of accidents where only one driver is involved.
Young drivers are particularly affected by the problem of drink driving because of their lack of experience and maturity as drivers.

Blood alcohol
The amount of alcohol in the blood is known as the blood alcohol level, measured by either a breathalyser or blood samples. Once in the blood, alcohol affects in particular the cells of the cerebral cortex, the command centre for movement and behaviour. This is why the presence of alcohol in the blood is dangerous: it leads to loss of self-control and problems with reflexes and vision.

After absorption of an alcoholic drink, the blood alcohol level peaks after 30 minutes if the alcohol is drunk on an empty stomach, and after 45 minutes to 1 hour if it is drunk with a meal. The elimination time depends on the quantity of alcohol ingested. It will take 4-5 hours for a blood alcohol level of 0.6 g/l to diminish to zero, that is to say an elimination rate of about 0.15 g/l per hour. This ethanol elimination is subject to wide variations depending on the individual; however, contrary to established ideas, neither cold nor physical effort accelerate elimination. A physical manual worker does not eliminate blood alcohol any more quickly than an office worker. If the drink is taken during a meal, the increase in blood alcohol level is slowed down and is reduced by about a third. Fatty foods (lipids) or sweet foods (carbohydrates) delay the rise in blood alcohol levels.

Alcohol and the nervous system
Alcohol can act as a stimulant and provoke a sensation close to euphoria; the subject wrongly assesses his capabilities, taking risks which would never have been taken in the normal state. Alcohol can also act like an anaesthetic: it suppresses or reduces perception, disrupts the faculties and, above all, slows down the reflexes. At 100 km/h, with a blood alcohol level of 0.8 g/l, the delay in response is approximately 0.5 seconds, such that the braking distance required is 14 metres greater than in a subject without alcohol.

Vision: Alcohol acts in several ways on the optic nerve, primarily on the process of transmission of images to the brain:

• false estimation of distances, leading to ill-advised overtaking,
• significant increase in dazzle when driving at night,
• reduction in the visual field: "tunnel" vision - dangerous at junctions.

Medications + alcohol: Some medications, in particular tranquillisers and stimulants, increase the effects of alcohol considerably: limited quantities of alcoholic drinks, tolerated without any great risk normally, become very dangerous (see Alcohol and medications).

Legislation
Refer to National legislation.