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Effects of alcohol on driving

Alcohol affects the ability to drive

What is alcohol?

When consumed in moderation, alcohol can be harmless. However, alcohol is notorious for being the most widely used social drug in Australia and is also known as a depressant drug that slows down the activity of the central nervous system, including the brain.

Healthdirect Australia reported that in the long run, frequent consumption of alcohol increases the risk of mental health issues and that abusing alcohol and other drugs can actually trigger a host of mental health issues.

Of course, there are several short-term effects of alcohol consumption that can potentially affect everyday activities such as driving.

How alcohol affects driving

As we recognise alcohol as a drug, it’s not advised for anyone to drive after having alcohol because it could affect your driving by causing the following:

  • Impaired vision
  • Reduced reaction times
  • Reduced concentration and vigilance
  • Feeling more relaxed and drowsy, which may cause a driver to fall asleep at the wheel
  • Difficulty in understanding sensory information
  • Difficulty multitasking (e.g. keeping in the lane and in the right direction while concentrating on other traffic)
  • Failure to obey road rules
  • Slurred speech
  • Overconfidence, which may lead to unnecessary risk-taking.

Additionally, alcohol causes nausea and vomiting and can still affect you the next day. The effects of a hangover after a night of drinking can make it hard for one to concentrate and drive safely, and can even cause you to fall asleep while driving.

With alcohol affecting our views and experience of reality, you may be unaware of how much your driving skills have been affected. A person who has been drinking alcohol may think that if they are especially careful, they will be able to drive safely – but that is usually always distorted by the effects of alcohol.

On top of that, recording a blood alcohol content (BAC) level of 0.05 and above while driving can lead to hefty fines while higher BAC recordings can land offenders in prison.

Impairment starts at low doses of alcohol

The US Department of National Highway Traffic Safety Administration (NHTSA) reviewed 112 studies and compiled their findings in ‘Effects of Low Doses of Alcohol on Driving Related Skills’. They found strong evidence that impairment of driving-related skills can begin from any BAC level above zero, as summarised below:


Tracking refers to our ability to control and maintain position relative to changes in our driving environment. Tracking errors can be contributors to run-off-road accidents or head-on crashes. Studies reported impairment at BACs as low as 0.0018 and consistently at 0.005.

Divided attention

This is the ability to concentrate on two or more tasks simultaneously and make decisions about them. Some studies showed people who drink could show signs of impairment to their divided attention at a BAC level as low as 0.005.


At BACs of at least 0.01, the time taken to fall asleep is significantly less than if you didn’t consume alcohol. So the drowsier you are, the more you are at risk of having a fatigue-related crash even if you are within the legal limit.

Reaction time

This refers to the time between the occurrence of an event or the appearance of an object and a person’s reaction to it if required. Studies indicated impairment of reaction time by alcohol at as low as 0.02%BAC.


In this context, vigilance is the level of alertness or watchfulness we can give to a task or an object in the driving environment. The studies showed that vigilance could be impaired at BACs of at least 0.03.


Visual functions include visual acuity (the ability to see fine details in objects), contrast sensitivity, eye movements, and motor control of the eye. For some visual functions, impairment started to become evident at BACs of about 0.03.


This refers to our ability to process and make sense of information presented to us whether through vision, hearing or what we feel. Research findings indicated perception impairment at BAC levels as low as 0.04.

Psychomotor skills

This refers to the ability to maintain balance and to perform and coordinate physical tasks. Studies found that balance can begin to become impaired at a BAC of 0.04. Complex tasks requiring coordination can be affected at 0.05.

Read more on the effects of alcohol and factors to consider before getting behind the wheel after a night of drinking from the Transport Accident Commission of Victoria.

Tips for driving safely

Don’t drive if you plan on drinking

You may not feel it immediately but even a little bit of alcohol can affect your ability to drive.

Keep track of how much you drink

Monitor the number of standard drinks you consume each hour to ensure you don’t go overboard. Everyone processes alcohol differently and it is possible for you to reach a high BAC level with just a few drinks. 

Use a breathalyser to know your BAC

There is no sure way of knowing your BAC other than with an alcohol breath test, and the most reliable way to know your BAC is through a personal breathalyser.

Limit your drinking

Start with a non-alcoholic drink, and have some water as a “spacer” every second or third drink.

Avoid topping up your glass, and drink low-alcohol content drinks while avoiding mixed drinks as it is difficult to tell how much alcohol they contain.

Try not to drink in shouts or rounds, so you don’t feel pressured to keep up with your friends. Instead, sip your drinks and avoid salty foods that could make you more thirsty.

Lastly, don’t overestimate your alcohol limits. Factors such as age, gender and body fat percentage can lead to faster spikes in BAC levels. Find out more about BAC, how it’s measured and the factors that affect it.

Wait for your BAC to drop

It is important to remember that BAC levels can continue to rise up to 3 hours after the last drink was consumed.

The only way to remove alcohol from your system is to allow the body time to process it. Showers, coffee or fresh air will not reduce BAC.

On average, the liver breaks down a little less than one standard drink per hour. Before driving, you should wait at least an hour for each standard drink you’ve had.

Test yourself with a breathalyser to be sure you aren’t above the legal BAC limit.

Have a backup plan

If you have had too much to drink, be prepared to make other arrangements, so you don’t have to drive to get home.

The best way to get home safely after a night out drinking is to make plans while sober before your night out drinking. Always plan around the fact that you are likely to be intoxicated to the point of impairment and will need a ride home.

Opt for e-hailing services, appoint a designated driver or have a family member pick you up once you’re ready to head home to avoid unwanted accidents when on the road.