How long after drinking can I drive?

A simple enough question but not quite so straightforward to answer.

Alcohol slows down the body’s reactions, which makes it unsafe to drive and puts you (the driver), passengers and the general public at risk. People under the influence of alcohol are more likely to take risks as inhibitions and urges are no longer repressed.

The effect of alcohol also varies from person to person, being influenced by a number of different factors, including:

• Weight, age and sex of the person (women are usually more affected by alcohol than men);
• Metabolic rate of the person;
• Type of alcohol drunk;
• Whether the person has eaten before drinking;
• Stress levels of the person.

So what is a ‘safe’ amount to drink if you are driving?

What is the drink drive limit?

The safest amount is of course zero, but in England, Wales, and Northern Ireland the limit is 80mg of alcohol per 100ml of blood; 107 mg per 100ml of urine; or 35 microgrammes of alcohol per 100 ml of breath.
In Scotland the limit is reduced to 50mg of alcohol per 100ml of blood; 67 mg per 100ml of urine or 22 microgrammes per 100 ml of breath.
Even just 10mg of alcohol per 100ml of blood in your system apparently makes you 37% more likely to be involved in a fatal road accident – a sobering thought!
But how does that translate in terms of your humble pint or cold glass of white? How many units can you drink and drive? How much is 1 unit of alcohol?
The size of the drink and the strength of the alcohol determines the number of units in a drink. Drink Aware campaign publish this helpful guide:

Put simply, a pint of low strength (3.6%) lager, beer or cider is 2 units; a pint of higher strength (5.2%) is 3 units. A standard glass (175ml) average strength wine (12%) is over 2 units; a large glass (250ml) is 3 units. A single measure (25ml) of spirits is 1 unit.

Returning then to the original question: how long after drinking can you drive? In order to break down and process the alcohol, the body uses mainly enzymes in the liver. If you suffer from liver damage or the liver isn’t functioning properly, this process can take longer.
The average adult takes about an hour to process one unit of alcohol. And there is nothing you can do to speed this up or eliminate the alcohol in your body.
Rough guidelines are:

• 8 pints of beer would take 17 hours from when you’ve stopped drinking before driving
• 1 bottle of wine would take 11 hours from when you’ve stopped drinking before driving
• 2 pints of lager and 2 pints of cider would take 172 hours from when you’ve stopped drinking before driving.

So you may even be over the limit, the morning after the night before. If you know you will be driving the next day, opt for lower strength drinks, smaller measures, non-alcoholic drinks (even alternate them with alcoholic ones), and stop drinking alcohol well before the end of the night to give yourself to process any alcohol in your body.