Question 1 of 20
If your vehicle hydroplanes, what should you do?
Correct. Release the accelerator and push in the clutch. Do not brake or steer hard until the tires regain contact.
California General Knowledge CDL Practice Test
This is a free 20-question practice test for the General Knowledge portion of the California Commercial Driver's License knowledge exam. Questions are pulled from a pool of 97 drawn from the AAMVA CDL Manual, which is the source document the California Department of Motor Vehicles uses to write its actual exam.
How it works: Click an answer. The correct choice highlights in green, and you'll see a short explanation. Aim for 85% or better before you sit for the real test in California.
Question 2 of 20
The most important reason for doing a vehicle inspection is to:
Correct. A pre-trip inspection is meant to find problems that could cause a crash or breakdown. Compliance is a side effect, not the purpose.
Question 3 of 20
On a tight curve in a rural mountain road:
Correct. Mountain curves often have advisory speeds well below your safe load speed. Slow before entering and use the full lane safely.
Question 4 of 20
How many red reflective triangles must you carry in your commercial vehicle for emergency warning?
Correct. You must carry three red reflective triangles, six fusees, or three liquid-burning flares for emergency warning use.
Question 5 of 20
On a 6-tire single vehicle, the maximum allowable air loss rate (engine off, brakes released) is:
Correct. For a single vehicle, no more than 2 psi per minute leakage with the engine off and brakes released. Combinations are limited to 3 psi/min.
Question 6 of 20
A driver who has been disqualified is:
Correct. A disqualified driver may not operate a commercial motor vehicle on public roads, regardless of supervision.
Question 7 of 20
A fully loaded tractor-trailer traveling at 55 mph on dry pavement requires roughly what total stopping distance (perception + reaction + braking)?
Correct. Total stopping distance for a heavy commercial vehicle at 55 mph on dry pavement is approximately 300 feet, or the length of a football field including end zones.
Question 8 of 20
Which of these is the best way to communicate that you are slowing down?
Correct. Lightly tapping the brake pedal flashes the brake lights, alerting drivers behind that you are slowing.
Question 9 of 20
How can you tell if you are driving in mountains?
Correct. Mountain driving demands attention to grade-related challenges: gear selection on upgrades, speed control on downgrades, escape ramp awareness.
Question 10 of 20
Communicating your intention to other drivers is best accomplished by:
Correct. Use turn signals well before turning or changing lanes. Brake lights, four-way flashers, and headlights also help communicate.
Question 11 of 20
What is the minimum tread depth required for the front (steering) tires of a commercial vehicle?
Correct. Steer-axle tires must have at least 4/32-inch tread depth in every major groove. Other tires require at least 2/32 inch.
Question 12 of 20
What is the only effective way to remove alcohol from the body?
Correct. Only time eliminates alcohol from the body — at roughly one drink per hour. Coffee, food, and showers do not speed up the process.
Question 13 of 20
You are about to drive a vehicle that you have not driven before. What should you do?
Correct. Federal regulations require the driver to be satisfied that the vehicle is in safe operating condition before driving. The previous driver's inspection does not relieve you of that responsibility.
Question 14 of 20
The blood-alcohol concentration (BAC) at or above which a CDL driver is considered to be driving under the influence in a commercial motor vehicle is:
Correct. The federal BAC limit for CDL drivers operating a commercial vehicle is .04 — half the .08 limit for non-commercial drivers in most states.
Question 15 of 20
A driver-side skid can cause a tractor-trailer to:
Correct. When the drive wheels lose traction and the trailer continues forward, the tractor pivots and the rig jackknifes.
Question 16 of 20
You are driving on a steep downgrade and your brakes have failed. The best escape is to:
Correct. If a runaway escape ramp is available, use it. Modern arrester beds use loose gravel or sand to slow the vehicle without injury to the driver.
Question 17 of 20
When merging onto a highway, you should:
Correct. Use the on-ramp to accelerate to traffic speed and merge into an existing gap. Stopping at the end of an on-ramp is dangerous.
Question 18 of 20
Which of these is true about driving in fog?
Correct. In fog, high beams reflect off water particles and impair vision. Use low beams. Many drivers also use four-way flashers when moving slowly to alert traffic.
Question 19 of 20
How often must drivers inspect their cargo and securing devices?
Correct. Federal rule: inspect within the first 50 miles, then every 150 miles or 3 hours of driving, whichever comes first, plus every change of duty status.
Question 20 of 20
A "low-clearance" warning sign requires the driver to:
Correct. Verify your vehicle's height. Hitting a low-clearance bridge or overpass is dangerous and expensive — and entirely the driver's responsibility.
About the California General Knowledge exam
Most state DMVs administer 50 General Knowledge questions and require 80% (40 correct) to pass. Questions are pulled from a much larger pool, so two applicants taking the test on the same day will see different mixes. The questions on this site are drawn from the AAMVA CDL Manual chapters that every state's exam is built from.
The California Department of Motor Vehicles follows the federal CDL standards established by FMCSA. To earn the General Knowledge credential, you must answer at least 80% of the questions correctly. Many candidates score lower the first time because the test pulls from a large pool — refreshing this page will give you a different mix of questions, drawn from the same authoritative source.
Want more practice? Try the full General Knowledge question bank or browse all California CDL practice tests.