CDL practice test: general knowledge

What the real test usually looks like

There is no single national CDL knowledge test. Federal rules set the knowledge areas every commercial driver must know, and each state builds and gives its own tests. The number of questions, the time limit and the way you take the test vary, and your state's CDL manual is the authority for yours.

• The federal knowledge areas. Federal regulations list twenty general areas that applicants must know, including vehicle inspections, basic control, shifting, backing, visual search, communication, speed and space management, night operation, extreme driving conditions, hazard perception, emergency maneuvers, skid control, cargo, hazardous materials, mountain driving, and fatigue and awareness (49 CFR 383.111).
• Washington's tests. Washington's licensing department lists the CDL general knowledge test (for classes A, B and C) as 50 questions with a passing score of 40, and separate tests for combination vehicles (20 questions), air brakes (25), passenger, school bus, doubles and triples, tank vehicles (20 each) and hazardous materials (30). It says you take the knowledge test before your skills test, and that a passed score is valid for 180 days (Washington DOL).
• Virginia's exams. Virginia's DMV says the general knowledge exam is required for all Class A, B and C drivers and is based on the manual's sections on driving safely and transporting cargo safely, plus a state supplement. Air brakes, combination vehicles and each endorsement (hazardous materials, tank, passenger, school bus, doubles and triples) have their own exams (Virginia DMV).
• The model manual. Virginia's manual is the CDL manual written by AAMVA for state licensing agencies. Its "Driving Safely" and "Transporting Cargo Safely" sections hold the general knowledge material, with review questions after each part (Virginia DMV manual).

Time limits vary. Washington's knowledge test page lists no time limit, for example. Check your state's manual or licensing website.

What our mocks cover. Our full mocks have 50 questions in 60 minutes on general knowledge, following the model manual's safe practice, in nine sections in this order: vehicle inspection (8 questions), basic control (5), seeing and communicating (5), speed and space (7), hazards and fatigue (6), night, weather and mountains (5), emergencies and skids (6), accidents and fires (3), and cargo and hazmat basics (5). You can go back and flag questions, and there is no calculator.

What they leave out. Air brakes, combination vehicles and endorsements are separate tests, and our mocks do not cover them. Rules that differ from state to state, such as your state's supplement, are not included, and there are no road sign images. Your state's CDL manual is the authority on anything that differs.

Question types with worked examples

One worked example for each main kind of question, with the trap most people fall into.

1. Numbers to remember. You stop on a one-way road. Where do the warning devices go? At about 10, 100 and 200 feet toward the approaching traffic. Trap: using the two-way road pattern, which puts devices both ahead and behind.

2. Following distance. A 40-foot vehicle at 35 mph needs how many seconds of space? 40 / 10 = 4 seconds, with nothing added because the speed is below 40 mph. At 50 mph it would be 5 seconds. Trap: adding the extra second at every speed.

3. Skids. In a front-wheel skid, the front of the vehicle keeps going straight however you turn the wheel. What stops it? Let the vehicle slow down: stop turning and braking so hard, and slow as quickly as you can without skidding. Trap: turning the wheel more, which does nothing while the front tires have no grip.

4. Fires. Which fire extinguisher is meant for electrical fires and burning liquids? The B:C type. The A:B:C type also works on burning wood, paper and cloth. Aim at the base of the fire, not up in the flames. Trap: using water on an electrical or fuel fire, which can cause a shock or spread the flames.

5. Cargo checks. When do you first recheck your cargo securement on a trip? Within the first 50 miles, then every 150 miles or every three hours, whichever comes first. Trap: choosing the larger number because it sounds more practical. Learn the exact figures from your manual.

How to prepare

1. Get your state's CDL manual. Questions come from it. Virginia's DMV, for example, says its exam questions are taken from the Virginia Commercial Driver's Manual (Virginia DMV). If your state has a supplement, read that too.
2. Find out which tests you need. Everyone takes general knowledge. Depending on your vehicle and class, you may also need air brakes, combination vehicles or endorsement tests, each with its own questions (Washington DOL).
3. Read the driving safely and cargo sections closely. They hold the general knowledge material. Answer the review questions at the end of each part and reread any part you miss (Virginia DMV manual).
4. Make a list of the numbers. Tread depths, following distance seconds, warning device distances, the 500-foot headlight rule, tie-down counts and cargo check times. Many questions turn on one number.
5. Learn the order of steps. What you do first in a skid, a tire failure, a brake failure or an accident. Questions often ask for the first or best action.
6. Choose the safest answer. The manual's answers favor slowing down, keeping space, warning others and stopping to check. If two answers look right, pick the more cautious one that follows the manual.
7. Practice at a steady pace. Our mocks give you 60 minutes for 50 questions, a little over a minute each. Take full timed mocks so you can finish with time to check your marked questions.

How scoring usually works

Scoring follows federal rules, applied by each state. Federal regulations say an applicant must answer at least 80 percent of the questions correctly to pass each knowledge test (49 CFR 383.135). Two public examples of how states apply it:

• Washington: 40 correct out of 50 on general knowledge, and a passed score is valid for 180 days (Washington DOL).
• Virginia: at least 80% of the general knowledge questions correct. You may take knowledge exams only once per business day, and passed results remain valid for one year from the test date (Virginia DMV).

Our practice score is the number of our own questions you answered correctly, with a breakdown by section, so you can see where to focus. It is a practice score: it is not a score on any state's test and does not predict whether you will pass.

Common CDL general knowledge test mistakes

• Mixing up the warning device patterns. Two-way roads: near the vehicle and about 100 feet ahead and behind. One-way or divided roads: 10, 100 and 200 feet toward approaching traffic.
• Forgetting the extra second. Following distance is one second per 10 feet of length, plus one second above 40 mph.
• Braking harder in a skid. In a drive-wheel braking skid, stop braking first so the wheels can roll, then counter-steer.
• Downshifting too late. Pick a low gear before the downgrade, not after speed builds.
• Mixing up tire rules. At least 4/32 inch on front tires and 2/32 inch on the others.
• Using one tie-down on small cargo. However small the load, use at least two.
• Studying the wrong book. Air brakes and combination vehicles have their own tests. For general knowledge, focus on the driving safely and cargo sections of your state's manual.