California CDL — General Knowledge Practice Test
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California CDL — General Knowledge questions with answers
20 sample questions from the California CDL — General Knowledge question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
1. Why is a high center of gravity (cargo loaded high or unevenly) dangerous?
Correct answer: It makes the vehicle more likely to roll over
A high center of gravity makes the vehicle more likely to tip over, especially in curves or during quick moves. Load heavier freight low and spread it out to keep the center of gravity low.
Source: California CDL Manual — Section 3: Transporting Cargo Safely
2. In many emergencies, which is quicker as a way to avoid a crash?
Correct answer: Steering around the hazard can be quicker than stopping
Stopping is not always the best move; you can often turn (steer) to miss an obstacle faster than you can stop for it. Keep a firm grip and make a smooth, quick steering move, then countersteer.
Source: California CDL Manual — Section 2: Driving Safely (Driving Emergencies)
3. When should you select a safe speed and a low gear for a long, steep downgrade?
Correct answer: Before you start down the grade
Choose your safe speed and shift into a low gear before you start down the grade. Once you are already descending, it may be too late to shift down safely.
Source: California CDL Manual — Section 2: Driving Safely (Controlling Your Speed)
4. What blood alcohol concentration (BAC) makes it illegal to operate a commercial vehicle?
Correct answer: 0.04 or higher
It is illegal to drive a commercial vehicle with a BAC of 0.04 or higher, which is stricter than the 0.08 limit for regular drivers. Even smaller amounts of alcohol impair driving skills.
Source: California CDL Manual — Section 2: Driving Safely (Alcohol, Other Drugs, and Driving)
5. Under the federal hours-of-service rules, how many hours may a property-carrying driver drive after 10 hours off duty?
Correct answer: 11 hours
After at least 10 consecutive hours off duty, a property-carrying driver may drive up to 11 hours. These limits are designed to reduce fatigue-related crashes.
Source: California Commercial Driver Handbook — Federal Requirements
6. When you are stopped on the side of the road or moving much slower than traffic, what should you turn on?
Correct answer: Your four-way emergency flashers
Turn on your four-way emergency flashers to warn other drivers. They tell approaching traffic that your vehicle is stopped or moving unusually slowly.
Source: California CDL Manual — Section 2: Driving Safely (Communicating)
7. Why should you never change gears while crossing railroad tracks?
Correct answer: You could miss a gear, stall, and get stuck on the tracks
Shifting on the tracks risks stalling or getting stuck if you miss the gear. Pick your gear before the crossing and keep moving steadily until you are all the way across.
Source: California CDL Manual — Section 2: Driving Safely (Railroad-Highway Crossings)
8. Which statement about speed limits for commercial vehicles is correct?
Correct answer: Never drive faster than is safe, and obey limits that may be lower for trucks
You must never drive faster than is safe for the conditions, and you must obey posted limits, which may be lower for trucks than for cars. Conditions such as rain, curves, or heavy traffic may require an even slower speed.
Source: California CDL Manual — Section 2: Driving Safely (Controlling Your Speed)
9. A sign posting a clearance such as "13 ft 6 in" at an underpass tells a truck driver what?
Correct answer: The maximum overhead clearance for your vehicle
It shows the maximum overhead clearance. Make sure your loaded vehicle's height is safely below the posted number, remembering that repaving or a tall load can reduce the real clearance.
Source: California CDL Manual — Section 2: Driving Safely (Managing Space)
10. When you turn left across oncoming traffic in a long commercial vehicle, what must you do?
Correct answer: Yield to oncoming traffic and allow extra time to clear the intersection
Yield to oncoming traffic and make sure you have enough of a gap, because a long, heavy vehicle takes extra time to clear the intersection. Do not turn unless you can complete it safely.
Source: California CDL Manual — Section 2: Driving Safely (Right-of-Way Rules)
11. When you must stop along the road, how soon should you put out your emergency warning devices?
Correct answer: Turn on flashers at once and set out triangles within 10 minutes
Turn on your four-way flashers immediately, then set out your warning triangles as soon as possible, within 10 minutes of stopping. This warns other drivers of your stopped vehicle.
Source: California CDL Manual — Section 2: Driving Safely (Accident Procedures)
12. When you have a choice, which direction should you back a large vehicle?
Correct answer: Toward the driver's (left) side, where you can see better
Back toward the driver's side whenever you can. You can see much better on that side by looking out the window, which reduces the chance of hitting something.
Source: California CDL Manual — Section 2: Driving Safely (Backing Safely)
13. If a fire breaks out in the cargo area of a sealed trailer, what should you NOT do?
Correct answer: Open the trailer doors to check on the fire
Do not open the trailer doors of a burning cargo box; letting in air can make the fire flare up. Keep the doors shut, park away from others, and wait for firefighters if you cannot safely fight it.
Source: California CDL Manual — Section 2: Driving Safely (Fires)
14. What is "perception distance" as part of total stopping distance?
Correct answer: The distance traveled from seeing a hazard until your brain recognizes it
Perception distance is how far your vehicle travels from the moment your eyes see a hazard until your brain recognizes it. It is separate from reaction distance, which is the distance traveled while you move your foot to the brake.
Source: California Commercial Driver Handbook — Driving Safely (Controlling Your Speed)
15. How does alcohol affect your ability to drive?
Correct answer: It slows reactions and impairs judgment, coordination, and vision
Alcohol slows your reactions and impairs your judgment, coordination, and vision. These are exactly the skills you need to control a large vehicle safely, so any amount raises crash risk.
Source: California CDL Manual — Section 2: Driving Safely (Alcohol, Other Drugs, and Driving)
16. If you are convicted of two serious traffic violations within three years, in separate incidents, how long is your CDL disqualified?
Correct answer: At least 60 days
Two serious traffic violations within three years lead to at least a 60-day disqualification; three within three years lead to at least 120 days. Serious violations include excessive speeding, reckless driving, and following too closely.
17. How do the convex (curved "spot") mirrors on a truck change what you see?
Correct answer: They make objects look smaller and farther away
Convex mirrors show a wider area but make objects look smaller and farther away than they really are. Remember this so you do not misjudge how close a vehicle actually is.
Source: California CDL Manual — Section 2: Driving Safely (Seeing to the Sides and Rear)
18. What should you do when driving through a work zone?
Correct answer: Slow down, watch for workers, and be ready to stop
Slow down, watch for workers and equipment, and be ready to stop. Work zones often have narrow lanes, sudden stops, and uneven surfaces, so extra care is needed.
Source: California CDL Manual — Section 2: Driving Safely (Work Zones)
19. Under federal rules, how may a commercial driver legally use a mobile phone while driving?
Correct answer: Hands-free only, without holding, reaching for, or dialing a handheld phone
Federal law allows only hands-free use with the phone within easy reach; holding the phone, dialing more than a single button, or reaching for it in an unsafe spot is banned. Texting while driving a commercial vehicle is also prohibited.
Source: California Commercial Driver Handbook — Driver Disqualifications
20. Who is responsible for making sure the cargo on a commercial vehicle is properly inspected and secured?
Correct answer: The driver of the vehicle
The driver is responsible for inspecting the cargo and making sure it is properly loaded and secured, even if someone else loaded it. You should also make sure it does not block your view or movement.
Source: California CDL Manual — Section 3: Transporting Cargo Safely