How alcohol affects your ability to drive safely ?

A drunk girl.

‘Joe, I think you’ve had one too many,’ the host says.

‘Who, me?’ Joe replies, slurring his words. ‘I can handle it!’

‘Maybe so, but I suggest you have a cup of coffee before you drive home.’

Good advice?

Definitely not!

Actually, if he’s had too much to drink, a cup of coffee will not make it safe for Joe to drive home; nor will a breath of fresh air, a cold shower, or exercise.

Such things may make Joe more awake.

But there’s only one thing that will help him to sober up—time.

To understand this better, it is helpful to take a look at how your body handles alcohol.

How alcohol affects your body?

When you drink an alcoholic beverage, the alcohol is quite “anxious” to get into your bloodstream.

Unlike other foods, it doesn’t need to be digested.

Some 20 percent immediately passes into your bloodstream through the walls of your stomach.

The rest is absorbed when it passes on to your small intestine.

The extent to which alcohol affects you depends upon how much it builds up in your bloodstream.

And how quickly it builds up depends upon several factors:

1. Amount of alcohol consumed:

How much alcohol do you consume with a typical drink?

Does a can of beer contain less alcohol than a shot of whiskey?

Surprising as it may seem, the typical serving of beer, table wine, and 80-proof whiskey all contain about the same amount of alcohol—a little more than a half ounce (15 cc).

Thus, the report Physiological Effects of Alcohol, published by the National Institute on Alcohol Abuse and Alcoholism, concludes:

In terms of the effects that drinking has on an individual’s mind and body, then, it does not really matter a great deal whether he or she chooses to drink wine, beer, or ‘hard liquor’—what is most important is the actual amount of alcohol consumed.”

2. Rate of absorption:

A number of factors can affect the rate at which alcohol is absorbed into your bloodstream.

Food is one factor.

That is, having food in your stomach tends to dilute alcohol and slow down its absorption.

So a person who has a glass of table wine with dinner will raise his blood alcohol level less than if he drank the same amount of alcohol on an empty stomach.

The spacing of drinks can also affect absorption.

Two drinks within a few minutes are much more intoxicating than two drinks taken over a couple of hours.

Weight is another factor.


Simply because the more a person weighs, the more fluid there is in his body to dilute alcohol.

For example, explains the report Development of a Traffic Safety and Alcohol Program for Senior Adults:

A person weighing 160 pounds [73 kg] has about 110 pounds [50 kg] of water in his/her body to dilute alcohol. After three drinks in an hour his/her BAC [blood alcohol content] would be about 0.07 percent. If an individual weighing 100 pounds [45 kg] drank the same amount in the same time, his/her BAC would be about 0.11 percent, and [he/she] would be eligible for arrest as a drunken driver.”

The alcohol concentration of the drink may also affect the absorption rate.

That is, the greater the alcohol concentration of the drink the quicker the alcohol will be absorbed.

So the absorption of alcohol into your bloodstream can be somewhat hastened or slowed—depending on any of the above influences.

However, there is one other factor that determines how much alcohol builds up in your bloodstream.

3. Oxidation rate:

Once alcohol is in your bloodstream, your body begins working to eliminate it.

A small percentage (between 2 and 10 percent) is given off unchanged in the breath, sweat, and urine.

The remainder is oxidized, “burned up,” mostly in the liver, where the chemical structure of the alcohol is changed to release heat and energy.

How quickly does your liver oxidize alcohol?

The rate of oxidation may vary slightly from person to person, depending upon such factors as weight and health.

According to the report by Malfetti and Winter,

as a general guide, a 150-pound [68-kg] person can oxidize (or ‘burn up’) the alcohol in one drink in one hour.”

How does alcohol build up in your bloodstream if your liver quickly swings into action to eliminate it?

It is simple:

When the absorption rate exceeds the oxidation rate, the blood alcohol level rises.

The report Physiological Effects of Alcohol illustrates it this way:

It’s much like bailing water out of a leaky boat: If alcohol ‘leaks’ into the blood faster than the body can ‘bail it out,’ its level, or concentration, rises.”

And as the blood alcohol level rises, the person gets increasingly intoxicated.

So while alcohol is rather “anxious” to get into the bloodstream, it takes its time about leaving.

The body will “burn up” the alcohol at its fixed oxidation rate.

And until it does, you should keep off the road.


Because alcohol affects you in several areas that are essential for the safe driving of an automobile.

How alcohol affects your driving?

You slip behind the steering wheel, start the engine, and off you go.

Driving may become second nature to you, especially if you’ve been doing it for years.

But it is not as simple as it may seem.

It has been estimated that under normal circumstances you make about 20 major decisions for each mile you drive.

Decisions about what you see and hear in connection with other cars, traffic signs, and pedestrians must be translated into actions involving the brake, the accelerator, the clutch, and the steering wheel.

And you don’t have much time to decide—often just a split second.

So driving requires a delicate coordination between decisions and actions.

Alcohol makes this driving task especially dangerous.


Because alcohol affects the driver in several ways that significantly impair his ability to drive safely..

1. Alcohol and vision

When you drive, it has been estimated, 85 to 90 percent of the information you obtain regarding the traffic situation is received through your eyes.

Your vision is controlled by a very delicate system of muscles that move and focus your eyes.

Alcohol slows the function of these muscles and thus impairs vision in several ways.

For one thing, alcohol reduces the ability of the eyes to control the amount of light entering the retina.

That’s especially critical at night.


Because it increases the amount of time it takes for the eye to recover from the glare of oncoming headlights.

Explains Alcohol, Vision & Driving, distributed by the American Automobile Association:

Normally, it takes one second for the pupil to constrict and respond to the glare of oncoming headlights. It takes seven seconds after exposure to headlight glare for the pupil to once again adapt to the dark conditions. This recovery action is slowed by alcohol.”

Consider the potential danger:

It is late at night.

You are driving on a winding, narrow highway—just one lane in each direction.

The glare of the headlights is blinding for drivers on both sides of the road.

How safe would you feel if you knew that the driver of an oncoming car had been drinking?

Alcohol also reduces peripheral vision—the ability, when looking straight ahead, to notice things on either side of you.

This is especially dangerous when mixing alcohol and high-speed driving.

Explains Alcohol, Vision & Driving:

Most drivers fail to realize that at 30 MPH [48 km/hr], a driver has reduced his side vision by 25%. At 45 MPH [72 km/hr], he has reduced his side vision by 50%. And at speeds over 60 MPH [97 km/hr], he is literally driving down a ‘vision tunnel.’”

Just imagine the possible consequences when the drinking driver speeds through intersections or past parked cars where a small child may suddenly dart out.

Moreover, alcohol can cause double vision, so that the drinking driver may see two cars approaching him instead of one.

Furthermore, it can affect a person’s ability to judge distance.

From all of this, it is evident that alcohol and driving, like oil and water, just don’t mix.

But accurately seeing the traffic situation around you is only part of what is involved in safely driving a car.

2. Alcohol and judgment

Once you perceive the traffic scene, you must judge, or decide, what action you are going to take.

For example, suppose you’re traveling on a two-way road, and the car in front of you is moving very slowly.

You must decide if and when it is safe to pass.

Here, too, alcohol can be deadly.

How so?

Often, as the drinker’s blood alcohol level rises, so does his self-confidence.

Explains the manual Alcohol and Alcohol Safety:

A person at this stage [.04 to .06 percent blood alcohol content] is likely to consider himself more alert and even more capable than normally even though there has been a reduction of his reaction time, his judgment, and his ability to respond to emergencies. Thus, as his actual ability to perform decreases, his confidence in this ability increases.”

As a result, the drinking driver may take more chances in passing or speeding.

Why, if the person is a poor or an inexperienced driver to begin with, even the slightest effect on his judgment could be dangerous!

3. Alcohol and reflexes

It’s bad enough that the drinking driver has trouble seeing and takes more risks.

What further compounds the problem is that alcohol also slows down his reaction time.

As a result, it may take just a fraction of a second longer for him to move his foot from the accelerator to the brake pedal.

To illustrate how dangerous that can be, the report by Malfetti and Winter notes that if you have just two 12-ounce (355-cc) cans of beer within an hour, your reaction time may be slowed by two fifths of a second.

Now, that may not sound like much.

But the report notes:

In two fifths of a second, an automobile traveling at 55 miles per hour (90 km/hr) will travel an additional 34 feet (10.4 m)!

Why, that could be the difference between a near-miss and a fatal accident!

When you consider how alcohol affects a person’s vision, judgment, and reflexes, it is easy to see why drinking and driving are a deadly combination.