CDL General Knowledge Test: The 20 Federal Topics and How to Study Them

What federal law puts on the CDL General Knowledge test

Federal rules list 20 general areas that every commercial driver must know, numbered (a)(1) to (a)(20) in 49 CFR 383.111. Your state builds its test from an FMCSA-approved question pool, with a prescribed number of questions from each area (383.133(b)). Those counts are not public, and the rule gives no percentages, so treat all 20 areas as fair game.

Every applicant takes this test, for Class A, B or C. It is scored on its own, and you need at least 80% (383.135(a)). The question count is your state's choice: Washington, for example, asks 50 questions and requires 40 correct, as checked on October 28, 2026. In AAMVA-model manuals, the material sits in Sections 1 to 3.

If you test in 2027, the list is the same. The 20 areas date from FMCSA's 2011 testing rule, and no rule published or proposed through October 2026 changes them. What can change is your state's manual edition and question count, so check both before you study.

The 20 federal areas in six CDL study blocks

Grouped by the kind of decision they ask for, the 20 areas fall into six blocks. The grouping is Passy's study aid; the area numbers are the federal ones.

Because federal rules give no weights, any split of study time is a judgment call. See how full CDL prep planned for launch sets 207 General Knowledge questions beside the other seven tests, then give extra time to the blocks you find hardest. The people in the scenarios below are fictional.

Block 1: vehicle controls, safety systems and inspections

This block asks whether a defect, reading or piece of equipment is acceptable, and what to do about it. The federal text names lights, horns, mirrors and fire extinguishers (383.111(a)(3)), and defects in tires, wheels, brakes, steering, suspension, exhaust, coupling and cargo (383.111(a)(17)).

Scenario. At 9 p.m., Dana's straight truck loses its alternator, and she stops on the shoulder of a divided highway. She turns on the hazard flashers right away. Within 10 minutes she sets her three warning triangles: one on the traffic side within 10 feet of the rear, one at 100 feet and one at 200 feet behind the truck, toward approaching traffic (49 CFR 392.22). On a two-lane road with traffic both ways, the placement changes: one within 10 feet of the truck, one about 100 feet behind and one about 100 feet ahead. Washington's guide adds a safety habit for the walk back: hold the triangles between yourself and oncoming traffic so drivers can see you.

Learn the two layouts as a pair. The free CDL practice questions include a breakdown on a two-lane road, so check your answer against both layouts.

Block 2: basic handling, shifting and backing

Scenario. Luis has to back his box truck into a loading dock, and he cannot see everything behind it. The manual's habits apply in order: get out and look at the path, use both mirrors, back slowly in the lowest reverse gear, and set up the move so he backs toward the driver's side, where he can see the rear through the side window. If a helper is available, they agree on hand signals first, including one for "stop" (Washington CDL Guide, 2.2.4). The tempting wrong answer is usually the fast one, such as backing to the right because it saves a trip around the block.

Turning belongs here too, since the basic-control area includes off-tracking (383.111(a)(4)). On a tight right turn, keep the rear close to the curb and turn wide as you finish, rather than swinging left first and inviting a car to pass on your right (Washington CDL Guide, 2.7.6).

Block 3: seeing, signaling and spotting hazards

The manual's look-ahead habit is 12 to 15 seconds, about a block at city speed and a quarter mile at highway speed (Washington CDL Guide, 2.4.1). Hazard perception covers road features and other road users (383.111(a)(13)), with clues such as a delivery driver about to step out of a double-parked van or a parked car showing brake lights or exhaust (Washington CDL Guide, 2.8.3).

Scenario. Priya sees brake lights flicker three cars ahead and a delivery van double-parked past them. She eases off early and checks her mirrors before she needs to change lanes. Questions in this block often set a late, dramatic action, such as a hard stop or a sudden swerve, against an early, smaller one. The manual's point is to spot hazards early enough to act calmly, so the early, smaller action is usually the one to look at first.

Block 4: speed management and following distance

The manual's following-distance rule is at least one second for every 10 feet of vehicle length below 40 mph, plus one second above 40 mph (Washington CDL Guide, 2.7.1). The same section warns that a slippery road needs much more space than the rule gives.

Scenario. Marco drives a straight truck about 30 feet long. At 35 mph he needs at least 3 seconds behind the car ahead, and at 60 mph at least 4.

The following and stopping distance guide works the rule for three rig lengths and shows how to count the gap. Numbers like these are easiest to keep when you drill them with their conditions, and flashcards on following distance by length and speed are planned for full CDL prep.

Block 5: night, weather, emergencies and mountain grades

This block tests order and timing: evasive steering, emergency stops, brake failure and blowouts (383.111(a)(14)), and the speed, gear and braking choices of mountain driving (383.111(a)(19)).

Scenario. A sign warns of a long downgrade ahead. Rosa downshifts to a low gear before the descent starts, not halfway down. On the grade she uses the manual's method: brake just hard enough to feel a definite slowdown, release when she is about 5 mph below her safe speed, and brake again when the speed climbs back to it (Washington CDL Guide, 2.16.4). Riding the brakes all the way down heats them until they fade.

Emergency steering has its own rule of order: you can almost always turn to miss an obstacle faster than you can stop, but not while braking, and the manual warns that top-heavy vehicles and tractors with more than one trailer may flip over in a quick turn (Washington CDL Guide, 2.17.1). Hazards and skids get a full treatment in the hazards, skids and emergencies guide, and grades, weather and rail crossings in the night, weather and mountain driving guide.

Block 6: cargo, alcohol, hazardous materials and fatigue

The last block asks whether you may drive at all, and what to check on the way. Safe operations regulations anchor it (383.111(a)(1)):

• Alcohol. A driver may not use alcohol within 4 hours before going on duty or driving (392.5(a)(1)). In a commercial vehicle, an alcohol concentration of 0.04 or more counts as driving under the influence (383.5).
• Cargo checks. The manual's rule is to inspect cargo securement within the first 50 miles of a trip, then every 150 miles or every 3 hours, whichever comes first (Washington CDL Guide, 2.1.6).
• Hazardous materials recognition. What counts as hazardous material needing an endorsement, the classes and placarding (383.111(a)(18)). The detail belongs to the HazMat endorsement test.
• Fatigue. When sleepy, stop and rest. The manual says the only safe cure is sleep (Washington CDL Guide, 2.11.2 and 2.11.5).

Scenario. Sam finishes a beer at 11 a.m. His shift starts at 2 p.m. That is 3 hours, so he may not go on duty before 3 p.m., however he feels, and even then not with any detectable alcohol in his system (392.5(a)(2)). The free practice set includes a similar timing question, so work it once you can count the four hours from the last drink.

The safe operations area also names the hours-of-service rules in Part 395. Washington's guide covers them in a short subsection of its introduction, so expect to learn them in more depth during training than the manual offers.

CDL General Knowledge numbers to memorize, and what is judgment

Some questions turn on a number and its condition, others on judgment. Learn each number as a full sentence, condition included.

Judgment questions ask you to rank actions: steer or brake, slow early or late, pull over or push on. Practice them by writing your own scenarios and explaining why the tempting answer is wrong. When you want explanations for every option, an explanation for every General Knowledge answer, right or wrong, is planned for full CDL prep. The vehicle inspection guide covers Block 1 in more depth, and the cargo guide covers the load checks in Block 6.