Blood Alcohol Concentration (BAC) is a measurement of alcohol in the blood.

It can be expressed using different units of volume and mass. For example, a BAC of 0.05 g/100 ml means that in every 100 ml of blood there are 0.05 grams of alcohol.

Many countries are enforcing BAC limits on drivers to reduce road traffic injuries. Police can stop any driver to check their BAC. All the driver has to do is breathe into a device called a breathalyser which detects how much alcohol is in his or her blood.

Drivers with a BAC of 0.05 g/100 ml are 40% more likely to get involved in a crash than those who haven’t consumed any alcohol. At a BAC of 0.1 g/100 ml the crash rate is almost four times higher, and even 20 times higher at a BAC of 0.15 /100 ml or more.

This combination of reduced ability and more risk taking is a dangerous mix!

Q: Why does alcohol have such an effect?

A: Alcohol is a nervous system depressant or a ‘downer’. It has a numbing effect on the brain making it slower and less able to concentrate.

Q: How soon does the effect of alcohol start?

A: After it enters your blood it only takes 10 minutes for alcohol to reach your brain.

Q: How much can I drink?

A: To stay safe do not drink at all when you will be driving. Research shows that a single drink increases the risk of death or serious injury by five times.

You do not have to be drunk for alcohol to affect your driving. Your driving abilities will be reduced even if you feel perfectly normal. If you are awake and can hold a conversation with your friends it does not mean that you can drive safely.

Q: What can help reduce the concentration of alcohol in my blood?

A: The only remedy to alcohol is time, allowing your body to break down the alcohol. The liver breaks down alcohol at a rate of approximately one standard drink per hour.

A standard drink is a drink which contains about 10 grams of alcohol. Restaurants usually serve alcohol in standard drink size glasses. Wine, however, is normally sold in 140 ml or 200 ml glasses. One 200 ml glass of wine contains approximately two standard drinks. Glasses used at home are likely to be bigger than the standard drink size. The labels on alcoholic drink bottles and cans sometimes show the number of standard drinks they contain.

Exercising, drinking coffee, taking cold showers, vomiting, fresh air, and other things can make you feel more alert but will not reduce your blood alcohol concentration.

The type of drug or medicine affects the way it influences driving:

• Medicines such as codeine and benzodiazepines (sleeping pills, tranquilisers, and anti-anxiety medications) can result in absent-mindedness as well as poor coordination and judgment and reduced ability to control the vehicle.
• Amphetamines, ecstasy, and cocaine are ‘uppers’ or stimulants; they make users feel more energetic and alert. So drivers drive faster and more aggressively and take more risks though their driving skills are reduced: they have less ability to control the vehicle, judge distances, coordinate their actions, and make sound decisions.
• Cannabis users feel relaxed and euphoric. They are ‘high’ or ‘stoned’. When translated into driving, this means their reaction time is longer, their coordination decreases, and their memory is affected.

Using drugs with or after drinking alcohol is never a good idea. People who combine alcohol and drugs are twice as likely to be involved in a crash as those drinking alcohol alone. Drivers with a BAC of more than 0.08 g/100 ml who combine drugs with alcohol are a hundred times more likely to be injured in a road crash.

Read more facts about drugs and driving