CDL General Knowledge Test · CDL General Knowledge Test
CDL General Knowledge Test: Hazards, Distractions, and Fitness to Drive Concepts
Importance ★★★★☆ · 11% (estimate)
Written by AI. Only units that passed a separate AI check (re-reading facts and numbers) are published. Tell us if you find a mistake.
Overview
This chapter covers seeing hazards before they become emergencies, and staying fit and focused enough to react to them. A hazard is any road condition or road user that could become a danger, such as a driver drifting toward an exit, a stopped delivery truck, or children playing near the road.
Move-over laws ask you to slow down and, when safe, change to a lane not next to an emergency vehicle or work zone on the roadside. Distracted drivers drift and change speed, so give them room. If an aggressive driver confronts you, get out of their way, avoid eye contact, and do not respond to gestures. Federal rules ban texting and hand-held phone use while driving a commercial vehicle, except to contact police or emergency services.
It is illegal to drive a commercial vehicle with a blood alcohol concentration of 0.04% or more, and any detectable alcohol below that puts you out of service for 24 hours. Only time sobers a person up. Fatigue is just as dangerous: when you are drowsy, the only real cure is to get off the road and sleep, and a short nap does more than a coffee stop.
Key concepts
Hazard
Any road condition or other road user (driver, bicyclist, pedestrian) that could become a danger. Seeing it early gives you time to plan a way out.
Memory tipA hazard is a possible emergency. Spot it early.
Move-over law
When you approach an emergency vehicle stopped on the roadside or a work zone, slow down and move to a lane not next to it if it is safe. If you cannot change lanes, slow down and pass with caution.
Memory tipLights on the shoulder: slow down and move over.
Phone and texting ban
Federal rules ban texting and using a hand-held mobile phone while driving a commercial vehicle. Using a hand-held phone is allowed only when needed to contact law enforcement or emergency services.
Memory tipHands on the wheel. Pull over to make calls.
Source: 49 CFR 392.80 and 392.82 (FMCSA) · as of 2026
CMV alcohol limit
Driving a commercial motor vehicle with a BAC of 0.04% or more is illegal. Any detectable alcohol below 0.04% puts you out of service for 24 hours.
Memory tipCommercial limit is 0.04%, and any alcohol means 24 hours off.
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 1 · as of 2026
Alcohol disqualification
A first offense (such as driving a CMV at 0.04% BAC or more, or refusing an alcohol test) means losing the CDL for at least 1 year, or at least 3 years if hauling placarded hazardous materials. A second offense means losing it for life.
Memory tip1 year, 3 with hazmat, life for a second offense.
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 1 · as of 2026
Fatigue
Sleep is the only cure for being tired. Warning signs include heavy eyes, constant yawning, drifting between lanes, and not remembering the last few miles. Pull off in a safe place and sleep or nap.
Memory tipCoffee is not sleep.
Often tested
- It is illegal to drive a CMV with a BAC of 0.04% or more.
- Any detectable alcohol under 0.04% means 24 hours out of service.
- Only time sobers you up. Coffee and fresh air do not.
- No texting or hand-held phone use while driving a CMV, except to call emergency services.
- When confronted by an aggressive driver, get out of the way and avoid eye contact.
- If you are sleepy, get off the road and sleep.
3 sample questions
Verified practice questions from this unit.
Question 1. What is the blood alcohol concentration (BAC) limit for driving a commercial motor vehicle?
- ① 0.08%
- ② 0.10%
- ③ 0.04%
▼ Show answer and explanation▲ Hide answer and explanation
Answer: ③ 0.04%
Key point: CMV alcohol limit is 0.04% BAC
It is illegal to drive a commercial motor vehicle with a BAC of 0.04% or more. That is half the limit most states use for regular drivers. Any detectable amount below 0.04% still puts you out of service for 24 hours.
Wrong choices
- 0.08%: 0.08% is the general limit for regular drivers, not for CMV drivers.
- 0.10%: This is much higher than the CMV limit.
Question 2. What is the only thing that sobers up a person who has been drinking?
- ① Time
- ② Black coffee
- ③ A cold shower and fresh air
▼ Show answer and explanation▲ Hide answer and explanation
Answer: ① Time
Key point: Only time sobers you up
The liver removes alcohol at a fixed rate. Only time will sober a person up. Coffee, fresh air, and cold showers do not work.
Wrong choices
- Black coffee: Coffee does not remove alcohol from the body.
- A cold shower and fresh air: These do not lower blood alcohol.
Question 3. Under federal rules, when may a CMV driver use a hand-held mobile phone while driving?
- ① When the call is from the employer
- ② Only when necessary to call police or other emergency services
- ③ Any time traffic is light
▼ Show answer and explanation▲ Hide answer and explanation
Answer: ② Only when necessary to call police or other emergency services
Key point: No hand-held phone while driving a CMV
Federal rules ban texting and hand-held mobile phone use while driving a CMV. The only exception is when you need to contact law enforcement or other emergency services. Pull off the road in a safe place to make other calls.
Wrong choices
- When the call is from the employer: Calls from your employer are not an exception.
- Any time traffic is light: Light traffic is not an exception.