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Tennessee driving lesson · Alcohol, Drugs & DUI

How alcohol wrecks your driving

A 3-minute lesson from the Tennessee course. Read the rules and examples, follow the handbook page references, and check your understanding before you move on.

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Read time
3 minutes
Course unit
Alcohol, Drugs & DUI
Checkpoint questions
6
Source pages
93, 94, 95, 97

Driving demands alertness, quick decisions and precise control — exactly what alcohol takes away. Judgment and vision, the two most important driving abilities, suffer after small amounts, and every extra drink multiplies your crash risk.

Crash risk compared to a sober driver

Crash risk compared to a sober driver
BACChance of causing a crash
.10 percent7 times more likely
.15 percent25 times more likely
.17 percent50 times more likely
Handbook p. 93 ↗

Alcohol's effects on driving ability

Alcohol's effects on driving ability
BACAbout how many drinksEffect
.01–.031 drink within 15 minutesRisk rises for young, low-tolerance drivers
.04–.072 drinks within 1/2 hourFeel high; some loss of judgment and control
.08 and above—Legal intoxication; definitely unsafe to drive
.10–.124 drinks within 2 hoursJudgment worse; crash risk 7 times normal
.13–.155–7 drinks within 3 hoursFar less muscle control; risk 25 times
.16–.258–12 drinks within 4 hoursConfused, need help standing; risk 50 times
Handbook p. 94 ↗

Know the rule

Everyone at .10 is too impaired to drive safely, and research shows skills, judgment and vision are greatly impaired at .03 to .04 — especially for young drinkers.

Handbook p. 94 ↗

Know the rule

Your ability to judge speed, time and distance changes after just one drink. Drinkers take needless risks: speeding, passing without enough room, taking curves too fast, showing off.

Handbook p. 94 ↗

How alcohol hurts your vision

  • Makes vision less clear
  • Cuts your ability to see at night by more than half
  • Worsens glare vision and slows glare recovery
  • Reduces side vision about 30 percent at .05 BAC
  • Distorts depth and distance judgment
Handbook p. 94 ↗

Know the rule

Your eyes supply almost 90 percent of the information you use in driving, so any vision loss can be disastrous.

Handbook p. 94 ↗

Know the rule

Reaction time and coordination are impaired at a BAC as low as .02.

Handbook p. 94 ↗

Know the rule

Alcohol is a depressant, not a stimulant. The 'lift' you feel comes from lowered inhibitions while it actually slows every nerve and body function.

Handbook p. 95 ↗

Did you know?

  • Judgment is the first thing alcohol affects
  • Two or three drinks in three hours or less impair most people's driving
  • Alcohol-related crashes are the number one killer of people under 40
Handbook p. 97 ↗

Put it into practice

After two drinks in half an hour, your friend says he feels fine and more alert than ever. That 'alert' feeling is the lowered inhibition of a depressant. His judgment and eye focus are already slipping — he shouldn't drive.

Check your understanding

Read the question, decide on an answer, then open it to check the explanation. These are Roadwise study questions based on the source handbook.

At a BAC of .10 percent, how much more likely are you to cause a crash compared to being sober?
  1. 2 times more likely
  2. 25 times more likely
  3. 7 times more likely
  4. 50 times more likely

Answer: 7 times more likely

At .10 percent BAC, you are about seven times more likely to cause a crash than if you were sober.

Handbook p. 93 ↗
At a BAC of .15 percent, your chances of causing a traffic crash increase to approximately:
  1. 7 times
  2. 2 times
  3. 50 times
  4. 25 times

Answer: 25 times

At .15 percent BAC, your chances of causing a crash increase to about 25 times that of a sober driver.

Handbook p. 93 ↗
At a BAC around .17 percent, how much more likely is a driver to cause a crash?
  1. 50 times more likely
  2. 10 times more likely
  3. 5 times more likely
  4. 100 times more likely

Answer: 50 times more likely

At around .17 percent BAC, a driver is about 50 times more likely to cause a crash than a sober driver.

Handbook p. 93 ↗
Driving skills, judgment, and vision can be measurably impaired starting at a BAC as low as:
  1. .08 percent
  2. .03 to .04 percent
  3. .15 percent
  4. .20 percent

Answer: .03 to .04 percent

Research shows driving skills, judgment, and vision are impaired at BAC levels as low as .03 to .04 percent.

Handbook p. 94 ↗
Reaction time and coordination begin to be impaired by alcohol starting at approximately what BAC?
  1. .08 percent
  2. .10 percent
  3. .02 percent
  4. .15 percent

Answer: .02 percent

Reaction time and coordination are impaired by alcohol consumption as low as .02 percent BAC.

Handbook p. 94 ↗
At a BAC of .05 percent, side vision is reduced by about:
  1. 5 percent
  2. 75 percent
  3. 10 percent
  4. 30 percent

Answer: 30 percent

Side vision is reduced by about 30 percent at just .05 percent BAC.

Handbook p. 94 ↗
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