Driving Under The Influence of Alcohol
How Alcohol Affects Your Driving Skills

The Effects of Alcohol on Your Driving Skills: Minimizing Driving Risks

Updated July 6, 2019

Your responsibilities as a driver and alcohol do not mix. As you will have learned already from our previous modules and your driver’s ed materials, a driver’s license comes with a legal and moral responsibility to do everything within your power to avoid injuring yourself, injuring other road users or damaging property. The only way to completely eliminate the risk of these events occurring is not to drive at all. Every time you get into the car, you entertain the risk of being involved in a crash.

However, the level of risk you are exposed to while driving is not constant and is largely within your control. Remember that driving is privilege which you will lose, if you do not do everything possible to minimize the risk of a traffic collision occurring.

Minimizing driving risks

Completing your driver’s education course and passing your test will set you on the road to becoming a safe driver but the journey does not end there. Throughout your driving life, you must continually recall and execute safe driving strategies to make every trip you take as risk-free as possible. If you drop the ball with these tactics for any reason (be it laziness, distraction or alcohol intoxication), you will start making more mistakes - any of which could prove to be fatal.

To minimize risk behind the wheel, you must always:

  1. 1

    Wear your seatbelt.
    Wear your seat belt and make sure your passengers wear theirs.

  2. 2

    Make your intentions known.
    Communicate with other road users where appropriate, using signal lights, hand signals and all other necessary means.

  3. 3

    Observe traffic control devices.
    Look for and abide by ALL road signs, traffic lights and pavement markings.

  4. 4

    Practice space management.
    Maintain a safe bubble of space around your vehicle.

  5. 5

    Drive defensively.
    Use defensive driving strategies to adjust your behavior for changing roadway conditions and predict problems before they occur.

  6. 6

    Control your vehicle.
    Use proper vehicle control techniques, such as gradual braking and assuming appropriate hand positions on the steering wheel.

  7. 7

    Stay alert.
    Monitor your physical and mental fitness to drive.

  8. 8

    Maintain your car.
    Keep your vehicle in good working order.

The mental effects of alcohol will render you more susceptible to forgetting these essential risk-reducing tasks. Even forgetting just one vital action could leave you in considerable danger. For example, you may jump into your car in the early evening when visibility is poor yet forget to switch on your headlights. This tiny oversight would make it very difficult for other road users to see your vehicle. Moreover, you could forget to signal prior to a lane change, causing the driver behind you to swerve and hit another vehicle. The chances of being involved in a collision increase dramatically when alcohol impairs your memory. If you have also forgotten to buckle up your seat belt, your chances of being seriously injured shoot up too.

Even if you remember every vital risk-reducing strategy while driving under the influence, there is a strong chance that alcohol’s physical effects will prevent you from executing those tasks effectively. You may steer too sharply, brake too suddenly, or miss the brake pedal altogether!

As discussed over previous modules of this section, even very small amounts of alcohol can impair your mental and physical driving ability. Studies have shown that motor skills, reaction time, reasoning ability, judgment, vision and awareness are all negatively affected by relatively low blood alcohol concentrations. Your ability to make rational decisions will be one of the first things to suffer when you start drinking. With poor decision-making skills, it is literally impossible to drive safely. Alcohol will leave you more likely to:

  • Underestimate the level of risk involved in a particular action or situation.
  • Disregard the laws of physics which govern the movement of your vehicle.
  • Overestimate your own driving skills, and your vehicle’s maneuvering ability.
  • Allow emotions rather the reasoning to determine the choices you make.
  • Become distracted by objects or situations in the car or on the roadway outside.

It is important to understand that there is no way to avoid making bad judgment calls while under the influence of alcohol. To do this, you would first have to recognize that you are intoxicated and incapable of thinking clearly – which would require good judgment. It is a situation in which safety and caution simply cannot win out over false confidence and the inability to see danger.

Always remember that the only “safe driving decision” you can make when you have consumed alcohol, is not to drive at all.

The effects of alcohol impairment on driving skills

A great deal of research has been conducted on alcohol-impaired driving. One study compared the driving behavior of a group of drivers while sober, with their behavior while intoxicated with different levels of alcohol. The results of their research showed that alcohol impaired drivers were:

  • More likely to overreact when correcting a skid
  • More inclined to brake harshly rather than steering around a hazard
  • Less aware of how fast they were traveling
  • Less able to maintain an appropriate lane position

Here is a break-down of how different BAC levels were shown to affect driving ability:

  • BAC of 0.02% to 0.05% - due to a reduction in information processing skills, drivers are less likely to see traffic control devices, important dashboard information and vulnerable road users such as cyclists and pedestrians.
  • BAC of 0.02% to 0.06% - the risk of drowsiness increases. Drivers are more likely to fall asleep or experience microsleep events while behind the wheel. This risk is increased considerably when driving at night or while already tired.
  • BAC of 0.02% to 0.08% - multitasking skills are affected. Drivers are more likely to make a mistake when managing various tasks consecutively.
  • BAC of 0.05% to 0.08% - tracking ability and muscle control are affected. Drivers are less likely to position themselves correctly within a lane and more likely to steer erratically, weave between lanes or leave the road altogether.

As you can see from these results, many of the drivers assessed during this study experienced quite a severe decline in driving ability with a BAC as low as 0.02%. It is also worth noting that the blood alcohol concentrations analyzed here are all below the legal limit of 0.08%.

Mental driving skills affected by alcohol

Alcohol’s ability to cloud cognition will begin within moments of your first sip. You will experience mood alterations and a decline in your ability to make sound judgments. As you continue drinking, your thought processes will slow down and eventually become confused. Soon, your vision will become blurred and your reaction time will be slowed to a degree that you are no longer capable of seeing and responding to hazards. Even if you do see them, the chances of you choosing an appropriate response with alcohol-impaired judgment are extremely slim.

Alcohol and judgment

Alcohol consumption significantly hinders your ability to make considered, logical choices. This effect begins to set in well before you reach the legal BAC limit. As you scan the roadway, you will be less able to comprehend the information your brain receives and more likely to choose an inappropriate response from the actions available to you.

For example, an intoxicated driver approaching an intersection as the light changes to red may decide to speed-up and rush across rather than coming to a stop. They are aware that this is both illegal and dangerous, but their brain assigns less importance to these things due to alcohol-impaired judgment. Instead, they think that increasing speed to get ahead of cross traffic is a reasonable risk to take – it is very unlikely they would ever reach this decision when sober!

Alcohol affects every judgment call you make while driving. This will include predicting the behavior of other drivers, and the outcome of hazardous situations. When you cannot predict what the road users around you will do, you become incapable of driving defensively to avoid upcoming conflicts.

The impact of alcohol on judgment is well-documented and has been identified as an issue, even at low BACs. Contrary to what you might expect, experienced road users make bad judgments while driving with alcohol in their systems, almost as frequently as novice drivers. With a BAC of 0.02% an experienced bus driver can be impaired to the degree that they will drive under bridges which are too low to accommodate their vehicle!

Young and inexperienced drivers are affected the most severely by alcohol-impaired judgment. Having less “driving information” stored in their memories will make them more likely to underestimate danger on the road. Plus, with limited life experience, teenagers are natural risk-takers. Adding alcohol into the mix and lowering their inhibitions further often results in incredibly reckless driving.

Attention and focus

Like impaired judgment, impaired focus and the inability to pay attention are among alcohol’s earliest effects. Blood alcohol concentrations as low as 0.02% have been shown to limit a person’s ability to consistently focus on a single task or manage various small tasks in succession. Alcohol will quickly make you less aware of objects and events in your immediate environment - which would be incredibly dangerous on a busy roadway.

While driving under the influence of alcohol, simple tasks such as changing lanes or coming to a complete stop will require far more concentration than usual. When your attention is monopolized by a single task, the chances of forgetting or overlooking another important task are high. For instance, while merging into a new lane, an alcohol-impaired driver may forget to check the area behind their vehicle and miss a motorcyclist in their blind spot. Or, they may be so preoccupied with completing this check that they forget to signal their intention to merge.

Driving requires continuous attentiveness to dozens of different tasks, like scanning the roadway ahead, checking your mirrors, monitoring your speed, signaling, shifting gears and managing the space around your vehicle, each of which are vital to your safety. Alternating your focus between these actions can be a serious mental strain, even when you’re sober! If alcohol has hindered your ability to focus to any degree, some essential task will eventually slip through the net. Remember, it only takes one silly mistake to cause a catastrophic collision.

Memory

Alcohol interferes with your ability to store new memories AND your ability to recall old memories. Studies have demonstrated this effect at BACs as low as 0.03%. Impaired memory is a serious problem for drivers, for two reasons:

  1. The inability to store new memories will mean important details are missed out while evaluating the road.
  2. The inability to recall old memories will hinder your decision making and judgment. Without access to your brain’s stored information on road rules, driving techniques and previous driving experiences, the choices you make will be insufficiently informed and quite often, dangerous.

Vision

Alcohol will have an adverse effect on your vision long before you notice any obvious blurring or “double-vision”. Within minutes of starting to consume alcohol, your ability to track moving objects will be impaired. Remember that while you are driving, all objects outside the vehicle will appear to be moving as you approach and pass them. As the effects of alcohol worsen, you will experience a decrease in clarity and ability to focus in on specific objects. This will make it harder to discern important information on the dashboard and on the roadway outside.

Sense of distance

As alcohol affects depth perception, you will be less able to accurately judge the distance between objects after drinking. This could cause you to leave an insufficient following distance, take turns too widely or overestimate how much space is available when merging into a new lane. You will also have trouble discerning how close objects by the roadside are, and the width of the road. You may think you have enough space to pass a tree overhanging the road, only to find you collide with its branches.

When a driver experiences depth perception impairment as a result of alcohol consumption, the greatest danger comes from the fact that objects usually appear further away than they truly are. This can lead you to misjudge braking distances and run into the back of other road users.

Sense of speed

It is very common for intoxicated motorists to drive at unsafe speeds without realizing it. Alcohol will make you less aware of your speed relative to other drivers and unable to judge the actual speed at which you are traveling. Furthermore, memory disturbances will mean you are less likely to check the speedometer regularly while driving. While under the influence of alcohol, you could end-up traveling twice as fast as you think you are and be completely incapable of stopping when you need to. If you cannot match the speed of other road users, it is also likely that you will unknowingly disrupt the flow of traffic and pose a hazard to other drivers.

Reaction time

Your reaction time is the total time it takes to see, consider and respond to a situation. The shorter your reaction time, the safer you will be while driving. If your reaction time is slowed as a result of alcohol consumption, you may overshoot stop lines, miss turn offs, rear-end other vehicles or collide with unexpected hazards. Reaction time can either be simple or complex.

  1. Simple reaction time is time is takes you to respond to an immediate situation. These reactions are reflexive and not proceeded by conscious consideration. For instance, flinching at the sound of gunshot or withdrawing your hand from boiling water are both simple reactions.
  2. Complex reaction time describes the time it takes you to consider a situation and choose from several possible responses. An example of this would be when a pedestrian steps out in front of your vehicle unexpectedly; you will have a moment or two to decide whether to brake, swerve or take some other action to avoid a collision.

Complex reaction time has been shown to suffer considerably at BACs of 0.04% to 0.08%. Drivers intoxicated at this level do react quickly, but generally not with the most appropriate action. For instance, they may slam on the brakes when a hazard appears in the roadway, rather than simply steering around it.

Alcohol consumption and space management

Application of the SEE space management system is a driver’s most effective safety strategy. The SEE system (or any similar space management system) allows you to search the roadway effectively, evaluate hazards and act to avoid potential problems before they turn into immediate dangers. Drinking alcohol disrupts each step of the SEE system, making it more difficult to perform and less effective overall.

  • Your ability to SEARCH the roadway will affected by vision impairment.
  • Your ability to EVALUATE what you have seen will be affected by cognitive impairment.
  • Your ability to EXECUTE appropriate maneuvers will be affected by impaired reaction time and sloppy motor skills.

Ineffective searching

The first step of the SEE space management system is searching the roadway. If you cannot perform this step effectively, the rest of the system becomes useless. Every decision you make and execute while driving is dependent on what you have seen, or think you have seen, during your roadway search. While impaired by alcohol, vision disturbances may cause you to overlook important details, confuse objects, misjudge distances and inaccurately gauge speed. If the information you have gathered is wrong, the decision you make is likely to be wrong too.

Remember that alcohol-impaired vision is not always obvious to the sufferer. It sets in at relatively low blood alcohol concentrations, impacting your ability to follow moving objects with your eyes. If you have had anything alcoholic to drink, always assume that your vision is impaired whether it feels impaired or not.

Roadway searches will always be less effective when you have consumed alcohol, because:

  • The muscles which control the movement of your eyes will be affected. Making it harder to alternate your gaze between objects. You will be more susceptible to object fixation, especially at higher speeds.
  • The coordination of your eye movement will be affected. Usually, the brain keeps eye movement synchronized. When brain-to-eye signals are disrupted by alcohol, your eye’s focal points may not be aligned, and you could experience double-vision.
  • You will experience poorer night vision. The pupils of your eye will not expand and contract in response to light changes so effectively, leaving you unable to see contrast, easily blinded by bright lights and unable to see in dark conditions.
  • Your peripheral vision will be narrowed, leaving you less able to spot objects and movement that is not in your central field of vision.
  • Your ability to distinguish between colors will be impaired. This could result in confusion and dangerous misinterpretation of road signs.

These impairments will worsen as your BAC rises, though many of them can occur at relatively low levels of alcohol intoxication. While searching the road, even a single missed or misinterpreted detail could result in a fatal evaluation error.

Inaccurate evaluation

Managing to gather accurate and complete information about the road environment would be nothing short of a miracle if you are under the influence of alcohol. Even if it were possible, the chances are high that you would be unable to complete the second stage of the SEE system effectively. During the evaluation stage, you will weigh-up the information you have gathered and choose an appropriate response. Selecting the safest action with the information you have relies on good judgment and unimpaired cognition, neither of which you will have if you’ve been drinking.

While there is alcohol in your system, you will be less able to:

Even if you could do all these things effectively, your alcohol impaired brain is liable to choose a wildly inappropriate course of action in response.

Execution errors

The final step of the SEE space management system involves executing your chosen response to the situation. If you have managed to make it through the search and evaluation stages while intoxicated, without incident (which is unlikely), things can still go very wrong as you attempt to carry out your maneuver. Even the most basic driving maneuvers become extremely challenging when you are under the influence of alcohol.

  • Your muscles will be less responsive, and your movements will be less precise.
  • Your ability to coordinate movement will be disrupted.
  • Your physical response time will be longer, meaning your body will not obey your brain as quickly as you need it to.

The combined effect of these motor skill-impairments could cause you to turn the steering wheel too sharply, or not sharply enough. You may brake too early or too late. Operating your signals and other vital in-car controls will be harder. If you are extremely intoxicated, you may even have trouble finding the pedals with your feet.

A defensive driving decision

In this  module, we have explored the profound, negative effect that alcohol consumption has on:

  • Physical driving skills
  • Mental driving skills
  • The ability to apply safety-enhancing strategies, like the SEE system

Moreover, we have seen how these detrimental effects take hold at relatively low blood alcohol concentrations, which are considerably under the legal limit of 0.08%. In a nutshell, this means that NO amount of alcohol is ‘safe’ when it comes to driving. As a defensive driver, you must always choose the safest course of action while behind the wheel and in any decisions relating to your physical and mental fitness to drive. If you have consumed alcohol, not driving at all is the safest course of action and therefore the only defensive driving decision you can make.

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