Alcohol, Drugs and Impaired Driving

How alcohol and drugs affect judgment, reaction time and vision, and why only time sobers a person up. Blood alcohol limits and penalties are set by each state and are covered on the state pages.

49 practice questions with answers. These rules are the same in every state.

Alcohol, Drugs and Impaired Driving quiz

Answer at your own pace. After each question you see the correct answer and why, and at the end a review of what you missed.

Quick quiz: 10 random questions on alcohol, drugs and impaired driving; pass with 8 correct.

Alcohol, Drugs and Impaired Driving questions with answers

Which ability does alcohol usually affect first?
1. Judgment and self control
2. Hearing
3. Sense of smell
4. Grip strength
Show answer

Answer A: Judgment and self control

Alcohol reduces judgment and inhibition before a drinker notices any clumsiness, which is why an impaired driver often feels perfectly capable while already driving worse.
What actually lowers the amount of alcohol in a person's blood?
1. Strong coffee
2. A cold shower
3. A large meal
4. The passage of time
Show answer

Answer D: The passage of time

The body eliminates alcohol at its own steady rate, so only time reduces blood alcohol. Coffee or a cold shower may make a person feel more awake while still impaired.
Which statement about standard drinks is correct?
1. A can of regular beer holds far less pure alcohol than a single shot of distilled spirits
2. Wine cannot cause impairment in the way that spirits do, because it is fermented rather than distilled
3. A standard serving of beer, of table wine and of distilled spirits each contain about the same amount of pure alcohol
4. Only distilled spirits raise blood alcohol, because the alcohol in beer and in table wine is too weak to have any effect
Show answer

Answer C: A standard serving of beer, of table wine and of distilled spirits each contain about the same amount of pure alcohol

Roughly 12 ounces of regular beer, 5 ounces of table wine and 1.5 ounces of 80 proof spirits each contain about the same amount of pure alcohol, so the type of drink does not change the effect.

Source: niaaa.nih.gov
Alcohol is classified as which kind of drug?
1. A stimulant that sharpens reflexes
2. A depressant that slows the central nervous system
3. A painkiller with no effect on driving
4. A nutritional supplement
Show answer

Answer B: A depressant that slows the central nervous system

As a depressant, alcohol slows the brain and nervous system, which lengthens reaction time and dulls the coordination that driving depends on.
How should you handle a prescription or over the counter medicine before driving?
1. Assume it is safe for driving because a doctor prescribed it
2. Assume anything sold without a prescription is safe for driving
3. Take a smaller dose so it cannot cause drowsiness
4. Read the label and ask a pharmacist or doctor whether it affects driving
Show answer

Answer D: Read the label and ask a pharmacist or doctor whether it affects driving

Many common medicines, including allergy and cold remedies, cause drowsiness or slowed reactions, and the label or a pharmacist can tell you whether driving is safe.
What happens when alcohol is combined with another drug that also affects the nervous system?
1. The two cancel each other out and leave the driver unimpaired
2. Impairment is often far greater than either one alone would produce
3. Only the stronger of the two substances has any effect on the driver
4. Alcohol leaves the body faster than it would on its own
Show answer

Answer B: Impairment is often far greater than either one alone would produce

Combined substances can multiply each other's effects, producing impairment well beyond what a driver would expect from either one taken separately.
You know in advance that you will be drinking at an event. What is the most reliable plan?
1. Arrange a driver who will not drink, or another way home, before the event begins
2. Eat a heavy meal before drinking and then drive home an hour or so later
3. Drink only beer instead of spirits, so that less alcohol reaches your blood
4. Decide at the end of the night whether you still feel able to drive yourself home safely
Show answer

Answer A: Arrange a driver who will not drink, or another way home, before the event begins

A decision made before drinking is not affected by alcohol, while judging your own fitness afterward relies on the very ability alcohol impairs first.
On a long drive you notice repeated yawning, missed exits and drifting toward the lane line. What should you do?
1. Open a window and turn up the radio
2. Drink coffee and press on to your destination
3. Pull off at a safe place and sleep, or change drivers
4. Increase your speed so the trip ends sooner
Show answer

Answer C: Pull off at a safe place and sleep, or change drivers

Those are warning signs that sleepiness is already interfering with driving, and only rest restores alertness. Fresh air, music and caffeine do not reverse it.

Source: nhtsa.gov
How does alcohol typically affect a driver's vision?
1. It improves night vision by widening the pupils of the eyes
2. It has no measurable effect on the eyes or on what the driver sees
3. It sharpens depth perception and makes distances much easier to judge at night
4. It blurs vision, weakens night vision and narrows attention to the sides
Show answer

Answer D: It blurs vision, weakens night vision and narrows attention to the sides

Alcohol slows the eye muscles and the brain's processing of what is seen, degrading focus, night vision, depth perception and awareness of movement at the edges of the field of view.
What does the implied consent law mean for drivers?
1. You may refuse any chemical test without penalty as long as you have not actually been drinking
2. Officers may search your vehicle at any time without a reason
3. You agree to carry proof of insurance whenever you are behind the wheel
4. By driving, you have agreed to a chemical test if lawfully arrested for impaired driving
Show answer

Answer D: By driving, you have agreed to a chemical test if lawfully arrested for impaired driving

Holding a license and driving on public roads is treated as consent to breath, blood or urine testing when an officer has grounds to arrest you. Refusing normally brings its own license penalties.

Source: nhtsa.gov
What do zero tolerance laws mean for a driver who is under 21?
1. They may drive with the same alcohol level that is allowed for adult drivers
2. They commit a violation at an alcohol level far below the adult limit
3. They may drive after drinking as long as they feel completely sober
4. They face no penalty unless a crash or an injury actually occurs
Show answer

Answer B: They commit a violation at an alcohol level far below the adult limit

Drivers under 21 may not legally drink, so every state sets a limit far below the adult one and treats even a trace reading as a violation. The exact figure is set by each state, and the penalty usually includes losing the license.

Source: nhtsa.gov
A driver's blood alcohol concentration is below the legal limit, but the driver is visibly impaired. Can the driver be arrested?
1. No, only a reading at or above the legal limit can lead to an arrest
2. No, unless the driver was involved in a crash with injuries
3. Yes, driving while impaired by alcohol is an offense at any concentration
4. Yes, but only if the driver holds a commercial license and is operating a commercial vehicle
Show answer

Answer C: Yes, driving while impaired by alcohol is an offense at any concentration

The per se figure, 0.08 percent in most states and 0.05 percent in Utah, is the level at which impairment is presumed. Impairment shown by driving behavior and field tests is enough on its own, because alcohol affects skills well before that number.

Source: nhtsa.gov
How does marijuana affect a driver?
1. It affects only drivers who have also been drinking alcohol at the same time
2. It sharpens concentration but slightly reduces night vision
3. It slows reaction time and impairs judgment of time and distance
4. It has no effect that can be measured while driving
Show answer

Answer C: It slows reaction time and impairs judgment of time and distance

Marijuana impairs coordination, attention and the ability to judge speed and distance. Driving while impaired by it is illegal everywhere, even where its use is legal.

Source: nhtsa.gov
How does eating a large meal before drinking affect impairment?
1. It soaks up the alcohol in the stomach so that almost none of it reaches the bloodstream
2. It prevents impairment as long as the meal is eaten first
3. It lets the liver break down the alcohol about twice as fast
4. It slows absorption but the alcohol still reaches the blood and impairs you
Show answer

Answer D: It slows absorption but the alcohol still reaches the blood and impairs you

Food delays how quickly alcohol enters the bloodstream, which can make the peak arrive later, but all of the alcohol is eventually absorbed.

Source: nhtsa.gov
About how much alcohol can the body eliminate per hour?
1. About one standard drink
2. About three standard drinks
3. About half a standard drink
4. It depends only on how much coffee is consumed
Show answer

Answer A: About one standard drink

The liver removes alcohol at a nearly fixed rate of roughly one standard drink per hour. Drinking faster than that raises the blood alcohol level, and nothing speeds the process.

Source: nhtsa.gov
Study tip. Rule out the options you know are wrong first. Two plausible answers are easier to choose between than four.
Two people drink the same amount of alcohol at the same time. Why might their blood alcohol concentrations differ?
1. The type of drink matters, because beer contains far less alcohol than wine
2. Only the time of day at which the drinks were consumed makes a difference
3. Body weight, gender and food in the stomach affect the concentration
4. The concentration is the same for everyone who drinks the same amount
Show answer

Answer C: Body weight, gender and food in the stomach affect the concentration

Smaller people and, on average, women reach higher concentrations from the same amount of alcohol, and an empty stomach speeds absorption. Counting drinks alone does not tell you your level.

Source: nhtsa.gov
What is the only reliable remedy for a driver who is sleepy?
1. Sleep
2. Strong coffee
3. Cold air from an open window
4. Loud music and singing
Show answer

Answer A: Sleep

Caffeine, fresh air and noise may make you feel alert for a few minutes, but they do not remove the need for sleep. Stop somewhere safe and rest.

Source: nhtsa.gov
Can a driver be charged with impaired driving after taking a legal over the counter medicine?
1. No, only illegal drugs and alcohol count as impairment
2. No, as long as the package was bought without a prescription
3. Yes, if the medicine impairs the ability to drive safely
4. Yes, but only if the medicine was recommended in writing by a doctor
Show answer

Answer C: Yes, if the medicine impairs the ability to drive safely

Impaired driving laws cover any substance that affects driving, including cold remedies, allergy pills and sleep aids sold without a prescription.

Source: nhtsa.gov
How do stimulant drugs such as amphetamines or cocaine typically affect driving?
1. They make the driver safer by fighting off drowsiness during long night trips
2. They improve reaction time enough to offset any other effects
3. They only affect driving after the stimulant effect wears off
4. They can make the driver overconfident and more willing to take risks
Show answer

Answer D: They can make the driver overconfident and more willing to take risks

Stimulants create a false sense of alertness and encourage aggressive, risky driving. When they wear off, sudden fatigue can follow.

Source: nhtsa.gov
How many alcoholic drinks does it take to begin affecting driving ability?
1. At least three drinks in an hour
2. About two drinks for an average adult
3. Even one drink can affect it
4. Enough to feel noticeably drunk
Show answer

Answer C: Even one drink can affect it

A single drink can slow reactions and weaken judgment before you feel any change. Impairment starts long before a person feels drunk.

Source: nhtsa.gov
You are very angry after an argument and about to drive. What should you know?
1. Strong emotions can impair judgment and attention much like alcohol
2. Driving is a good way to calm down because it forces you to think clearly
3. Anger improves alertness and shortens reaction time
4. Emotions do not affect driving unless you are also tired
Show answer

Answer A: Strong emotions can impair judgment and attention much like alcohol

Anger, grief and stress pull attention inward and encourage risk taking. Give yourself time to settle down before getting behind the wheel.
A friend who has been drinking insists on driving home. What is the right thing to do?
1. Let the friend drive slowly on quiet streets only
2. Take the keys and arrange a sober ride, even if the friend objects
3. Follow behind in your own car to keep an eye on the friend
4. Give the friend coffee and wait fifteen minutes before letting them drive
Show answer

Answer B: Take the keys and arrange a sober ride, even if the friend objects

An impaired driver is dangerous on any street at any speed, and coffee does not lower blood alcohol. Keeping the keys and finding another way home is the only safe choice.

Source: nhtsa.gov
As a driver keeps drinking, in what order are driving abilities usually lost?
1. Coordination, then vision, judgment and reaction time
2. Vision, then coordination, judgment and reaction time
3. Judgment, then vision, reaction time and coordination
4. Reaction time, then judgment, coordination and vision
Show answer

Answer C: Judgment, then vision, reaction time and coordination

Alcohol reaches the parts of the brain that handle judgment first, and only later does it visibly affect sight, reactions and muscle control.

Source: nhtsa.gov
How does alcohol change the time a driver needs to respond to a hazard?
1. It slows it, so stopping takes longer
2. It speeds it up while making the movements less accurate
3. It leaves it untouched until the legal limit has been passed
4. It slows it only when the driver is also short of sleep
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Answer A: It slows it, so stopping takes longer

Alcohol is a depressant that lengthens the time between seeing a hazard and acting on it, which adds directly to the distance needed to stop.

Source: nhtsa.gov
Which effect appears as a drinker's blood alcohol level climbs well past the first drinks?
1. Better concentration on one driving task at a time
2. Sharper depth perception in low light conditions
3. Faster and smoother responses to sudden hazards
4. Loss of muscle control and steady steering
Show answer

Answer D: Loss of muscle control and steady steering

Higher levels of alcohol reach the parts of the brain that control movement, which shows up as clumsy steering, late braking and poor lane control.

Source: nhtsa.gov
How does alcohol affect a driver's ability to handle several things at once?
1. It helps the driver focus on one thing at a time safely
2. It cuts the ability to divide attention between tasks
3. It has no effect at all until coordination is affected
4. It improves lane tracking while slowing hazard reaction
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Answer B: It cuts the ability to divide attention between tasks

Driving means watching the road, the mirrors and the instruments together, and alcohol narrows attention so that one of those tasks is dropped without the driver noticing.

Source: nhtsa.gov
A driver who has been drinking has two cups of strong coffee. What has changed?
1. Caffeine makes the liver clear the alcohol more quickly
2. The blood alcohol level falls by roughly one standard drink
3. The coffee cancels out the effect of the last drink taken
4. The driver is more awake but just as impaired
Show answer

Answer D: The driver is more awake but just as impaired

Coffee can make a drinker feel alert, but nothing except time removes alcohol from the blood, so a wide awake drinker is still an impaired driver.

Source: nhtsa.gov
Someone stops drinking heavily at two in the morning and drives to work at eight. What is true?
1. They may still be impaired and over the limit
2. Sleep clears alcohol from the body faster than being awake
3. Alcohol is always gone after a full night of sleep in bed
4. A shower and a large breakfast will finish clearing it out
Show answer

Answer A: They may still be impaired and over the limit

The body removes alcohol at a slow, fixed rate, so a heavy night can leave a driver impaired well into the next morning no matter how they feel.

Source: nhtsa.gov
A mixed drink is made with two shots of spirits. How much alcohol is that?
1. About one drink, because it is served in a single glass
2. About one drink, because the mixer dilutes the alcohol
3. About two standard drinks
4. About half a drink, since spirits are sipped very slowly
Show answer

Answer C: About two standard drinks

A standard drink is a fixed amount of pure alcohol, so a glass poured with two measures counts as two drinks however it is served.

Source: nhtsa.gov
Which of these does NOT affect how fast alcohol reaches the bloodstream?
1. How confident the drinker feels
2. Whether there is food in the stomach at the time
3. How quickly the drinks are taken one after another
4. How much alcohol each of the drinks contains
Show answer

Answer A: How confident the drinker feels

Food, the strength of the drinks and the speed of drinking all change how fast alcohol is absorbed, but a drinker's confidence changes nothing at all.

Source: nhtsa.gov
Two drivers each have three drinks, one over three hours and one in half an hour. What is the difference?
1. Neither is affected, because three drinks is a small amount
2. They reach exactly the same level, since the amount is equal
3. The fast drinker reaches a higher peak level
4. The slow drinker ends up more impaired by the end of the night
Show answer

Answer C: The fast drinker reaches a higher peak level

The liver removes alcohol at a steady rate, so drinking faster than the body can clear it pushes the blood alcohol level much higher.

Source: nhtsa.gov
What does a blood alcohol concentration of 0.08 mean for the driver of a car?
1. It is the level at which impairment first begins to appear
2. It is the level almost every state treats as legally intoxicated
3. It is a level that applies only to drivers who are under 21
4. It is a level that matters only if the driver causes a crash
Show answer

Answer B: It is the level almost every state treats as legally intoxicated

In almost every state a driver at 0.08 or above is legally intoxicated whatever the driver seems like, but impairment starts well before that level is reached.

Source: nhtsa.gov
How does the blood alcohol standard for a driver operating a commercial vehicle compare with the one for a car driver?
1. It is the same 0.08 standard that applies to car drivers
2. It is higher, because of the training commercial drivers get
3. There is no standard while the commercial driver is off duty
4. It is lower, set at 0.04
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Answer D: It is lower, set at 0.04

Commercial drivers are held to a stricter standard of 0.04 because of the size of their vehicles and the risk they carry.

Source: nhtsa.gov
A driver stopped on suspicion of impaired driving refuses to take a chemical test. What happens?
1. Nothing at all, because a driver may always refuse a test
2. The refusal is allowed once in any twelve month period
3. The refusal replaces any criminal charge with a small fine
4. A license penalty follows for the refusal itself
Show answer

Answer D: A license penalty follows for the refusal itself

Under implied consent, holding a license means agreeing to testing, so a refusal brings its own suspension separately from anything the court decides.

Source: nhtsa.gov
Besides a chemical test, what else supports an impaired driving charge?
1. Only the numbers produced by a laboratory blood analysis
2. The officer's observations of the driving and the driver
3. Only the number of drinks that the driver admits to having
4. Only a written statement from a passenger in the vehicle
Show answer

Answer B: The officer's observations of the driving and the driver

Weaving, slow responses, speech and balance observed by the officer are evidence in their own right, which is why a driver can be charged on behavior alone.

Source: nhtsa.gov
Which common non-prescription medicine is most likely to make a driver drowsy?
1. A plain pain reliever taken for an ordinary headache
2. An antacid tablet taken after eating a very heavy meal
3. A cold or allergy remedy containing an antihistamine
4. A vitamin supplement taken with breakfast each morning
Show answer

Answer C: A cold or allergy remedy containing an antihistamine

Antihistamines in cold and allergy remedies are a leading cause of drowsiness behind the wheel, which is why the label carries a warning.

Source: nhtsa.gov
Cannabis is legal for adults in some states. What does that mean for driving?
1. A small amount before driving is acceptable where it is legal
2. It only counts as impairment when mixed with alcohol as well
3. Driving while impaired by it is still an offense
4. It is treated as a medicine and does not affect driving skill
Show answer

Answer C: Driving while impaired by it is still an offense

Legal possession has nothing to do with driving law, and every state treats driving while impaired by cannabis as an offense.

Source: nhtsa.gov
How long can cannabis affect a driver?
1. For hours after the strongest effects have passed
2. Only while the person still feels obviously affected by it
3. Only for the few minutes while the smoke is in the room
4. Until the person has eaten a full meal and had some water
Show answer

Answer A: For hours after the strongest effects have passed

Slowed reactions, poor tracking and weak judgment of distance can last for hours, well beyond the point where the user believes the effects are over.

Source: nhtsa.gov
What is a microsleep?
1. A short nap deliberately taken at a highway rest area
2. A brief loss of hearing brought on by hours of driving
3. A short daydream that the driver can end at any moment
4. A few seconds of sleep, sometimes with the eyes open
Show answer

Answer D: A few seconds of sleep, sometimes with the eyes open

A microsleep is an involuntary lapse of a few seconds during which the driver is asleep and the vehicle travels blind, often without the driver knowing.

Source: nhtsa.gov
When is a driver at the highest risk of falling asleep at the wheel?
1. Only during the first hour after the sun has gone down
2. Late at night, early morning and mid afternoon
3. Only during the first hour of a long journey by road
4. Evenly through every hour of the day and of the night
Show answer

Answer B: Late at night, early morning and mid afternoon

The body clock produces its deepest dips in alertness in the small hours and again in the middle of the afternoon, and crash records follow those dips.

Source: nhtsa.gov
You feel drowsy, so you open a window and turn the radio up. What does that achieve?
1. It restores full alertness for the remainder of the trip
2. Very little, because the drowsiness comes back
3. It works about as well as a nap of twenty minutes would
4. It prevents microsleeps from happening for about an hour
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Answer B: Very little, because the drowsiness comes back

Cold air and loud music are not sleep, so the alerting effect lasts a minute or two and the driver is soon just as sleepy and closer to a lapse.

Source: nhtsa.gov
You stop at a rest area because you are sleepy. How long a nap is usually recommended?
1. About two minutes, just long enough to close your eyes
2. At least three hours, or the nap will have no value
3. Exactly one hour, in order to complete a sleep cycle
4. About fifteen to twenty minutes
Show answer

Answer D: About fifteen to twenty minutes

A short nap of fifteen to twenty minutes restores useful alertness without leaving the grogginess a longer sleep can bring, and you should wait a few minutes before driving on.

Source: nhtsa.gov
How does going a long time without sleep compare with drinking?
1. It can impair a driver in much the same way
2. It slows reactions but leaves judgment completely intact
3. It affects only drivers who are older than about sixty
4. It matters only on journeys longer than about five hours
Show answer

Answer A: It can impair a driver in much the same way

Long periods awake produce slow reactions, poor judgment and lapses of attention that resemble the effects of alcohol, which is why fatigue counts as impairment.

Source: nhtsa.gov
Which of these is an early warning that you are too tired to keep driving?
1. Wanting to stop for fuel before the tank runs low
2. Feeling hungry after several hours on the road
3. Not remembering the last few miles you drove
4. Noticing that the traffic around you has got heavier
Show answer

Answer C: Not remembering the last few miles you drove

Memory gaps, repeated yawning, heavy eyelids and drifting are the body signaling that sleep is winning, and they mean stop rather than push on.

Source: nhtsa.gov
What is a designated driver?
1. Someone who agrees to drink nothing at all
2. The person in the group who drinks the least that evening
3. The person who stops drinking an hour before leaving
4. The person who feels least affected at the end of the night
Show answer

Answer A: Someone who agrees to drink nothing at all

A designated driver drinks no alcohol whatsoever, because any amount begins to affect judgment and the whole point is a sober driver.

Source: nhtsa.gov
Study tip. When two answers both seem legal, pick the one that is safer for everyone on the road. That is how most tests are written.
When should you arrange your way home if you plan to drink?
1. After you see how the evening turns out for everyone
2. As soon as you start to notice the effects of drinking
3. Before the first drink
4. Once the party is over and you know who is still sober
Show answer

Answer C: Before the first drink

Judgment is the first thing alcohol weakens, so the plan has to be made while you can still make a good one.

Source: nhtsa.gov
The only person offering you a ride home has been drinking. What should you do?
1. Ride in the back seat, which is the safest place to be
2. Do not get in; find another way home
3. Ride along and help out by watching the road ahead
4. Ride only if the trip home is a short distance away
Show answer

Answer B: Do not get in; find another way home

A passenger in an impaired driver's vehicle shares all of the risk and can do nothing about it from the seat, so the only safe answer is another ride.

Source: nhtsa.gov
You are hosting a party and a guest who has been drinking wants to drive home. What should you do?
1. Serve coffee and food for the last hour of the evening
2. Let the guest decide, since adults know their own limits
3. Ask the guest to wait thirty minutes and then drive home
4. Stop serving and arrange a ride or a bed
Show answer

Answer D: Stop serving and arrange a ride or a bed

Only time removes alcohol, so a host who wants to prevent a crash has to remove the driving, not try to speed up sobering that cannot be sped up.

Source: nhtsa.gov
You feel fine twenty minutes after your last drink. Why is that a poor guide to driving?
1. Your level always peaks the moment you stop drinking
2. Your blood alcohol level can still be rising
3. Your level begins falling within five minutes of the drink
4. Your level stays exactly where it is until the next morning
Show answer

Answer B: Your blood alcohol level can still be rising

Alcohol keeps being absorbed for some time after the last drink, so a driver who feels able at the door can be more impaired a few miles down the road.

Source: nhtsa.gov