Which CDL applicants must pass the general knowledge test?

All Class A, B and C applicants

Only drivers seeking endorsements

When stopped on a two-lane, two-way road, where should you place your three warning triangles?

Within 10 feet of the rear on the traffic side, about 100 feet behind and about 100 feet ahead

All three directly behind the vehicle

50 feet behind, 100 feet behind and 200 feet behind

Before starting down a long, steep downgrade, you should:

Select a low gear before starting down the grade

Use the brakes continuously all the way down

CDL General Knowledge Test: How to Pass and Get Your CLP

The CDL general knowledge test is the written exam every commercial driver must pass, for Class A, B or C, before getting a commercial learner's permit (CLP). In most states it has 50 multiple-choice questions and requires 80% to pass. It covers vehicle inspection, safe driving, space and speed management, hazards, emergencies, cargo, and alcohol and drug rules from your state's CDL manual.

Updated on 2026-11-06 · Ver en español

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CDL general knowledge quiz: 5 questions

Which CDL applicants must pass the general knowledge test? Only Class A / Only Class A and B / All Class A, B and C applicants / Only drivers seeking endorsements. Answer: All Class A, B and C applicants. The general knowledge test is required for every CDL class. Additional tests are required for air brakes, combination vehicles and each endorsement.
You drive a 40-foot vehicle at 50 mph. How much following distance should you keep? 2 seconds / 3 seconds / 4 seconds / 5 seconds. Answer: 5 seconds. The CDL manual rule is one second for every 10 feet of vehicle length below 40 mph, plus one second above 40 mph: 40 ÷ 10 = 4, plus 1 = 5 seconds.
When stopped on a two-lane, two-way road, where should you place your three warning triangles? All three directly behind the vehicle / Within 10 feet of the rear on the traffic side, about 100 feet behind and about 100 feet ahead / 50 feet behind, 100 feet behind and 200 feet behind / Only one, 500 feet behind. Answer: Within 10 feet of the rear on the traffic side, about 100 feet behind and about 100 feet ahead. Place them within 10 minutes of stopping: one about 10 feet from the rear on the traffic side, one about 100 feet behind and one about 100 feet ahead. On a divided highway, place them 10, 100 and 200 feet behind.
What is the BAC limit for a driver operating a commercial motor vehicle? 0.02% / 0.04% / 0.05% / 0.08%. Answer: 0.04%. Federal rules set 0.04% for commercial drivers. Any detectable alcohol, or drinking within 4 hours before duty, puts the driver out of service for 24 hours.
Before starting down a long, steep downgrade, you should: Shift to neutral to save fuel / Select a low gear before starting down the grade / Use the brakes continuously all the way down / Speed up to get it over with. Answer: Select a low gear before starting down the grade. Shift into the right low gear before the downgrade and let engine braking do most of the work, using the service brakes only to control speed.

What the CDL general knowledge test is

A commercial driver's license (CDL) is required to drive large or heavy vehicles, vehicles that carry 16 or more people (including the driver) and vehicles carrying placarded hazardous materials. CDLs are issued by states under federal standards set by the Federal Motor Carrier Safety Administration (FMCSA), so the tests are very similar everywhere.

The general knowledge test is the first exam for all three CDL classes. In most states it has 50 questions and requires 80% (40 correct) to pass. The questions come from the general knowledge section of your state's CDL manual. You will usually take other knowledge tests at the same visit, depending on the class and endorsements you want.

CDL classes
Class	What you can drive	Examples
A	Combination vehicles with a gross combination weight rating of 26,001 lbs or more, towing a unit over 10,000 lbs	Tractor-trailers, truck and trailer combinations
B	Single vehicles with a gross vehicle weight rating of 26,001 lbs or more, towing 10,000 lbs or less	Straight trucks, large buses, dump trucks
C	Vehicles not in Class A or B that carry 16+ people including the driver, or placarded hazardous materials	Small passenger vans and buses, small hazmat vehicles

How to get your commercial learner's permit (CLP)

Passing the required knowledge tests earns you a commercial learner's permit (CLP). With a CLP, you may practice driving a commercial vehicle only with a CDL holder of the proper class and endorsements in the front seat. Federal rules require you to hold the CLP for at least 14 days before taking the skills test, and a CLP is valid for no more than one year.

Age: at least 18 to drive within your state (intrastate) and 21 to drive across state lines (interstate) or haul placarded hazardous materials.
A valid driver's license from your state of residence, plus the identity and residency documents your state requires.
A DOT medical exam by a certified medical examiner listed on the FMCSA National Registry. The medical certificate is valid for up to 24 months.
Self-certification of the type of commerce you will operate in (interstate or intrastate, excepted or non-excepted).
Entry-Level Driver Training (ELDT): since February 7, 2022, first-time Class A or B applicants, drivers upgrading their class and those seeking the passenger, school bus or hazmat endorsements must complete training from a provider listed on FMCSA's Training Provider Registry before the skills or hazmat test.
The skills test: a vehicle inspection, basic control maneuvers and an on-road drive, in a vehicle representative of your class.

Federal rules also require commercial drivers to read and speak English well enough to talk with the public, understand road signs, respond to officials and complete reports. Since June 2025, roadside inspectors enforce this as an out-of-service violation.

Other knowledge tests and endorsements

Most applicants take more than one knowledge test. Plan to study the sections for your class and any endorsements at the same time as the general knowledge section.

Common CDL knowledge tests
Test / endorsement	Who needs it
Air brakes	Drivers of vehicles with air brakes; failing it adds an air-brake restriction
Combination vehicles	Class A applicants
H — Hazardous materials	Drivers hauling placarded hazmat; also requires a TSA security threat assessment
N — Tank vehicle	Drivers of tank vehicles carrying liquids or gases in bulk
P — Passenger	Drivers of vehicles carrying 16+ people, including the driver
S — School bus	School bus drivers; requires the P endorsement too
T — Doubles/triples	Class A drivers pulling double or triple trailers
X — Tank and hazmat combined	Drivers who need both N and H

Key topics: inspection, seeing and space management

The general knowledge test is heavy on practical safety rules and numbers. Learn these well:

Vehicle inspection: pre-trip, en-route and post-trip inspections are required. Front tires need at least 4/32 inch of tread depth in every major groove; other tires need 2/32 inch.
Seeing ahead: look 12 to 15 seconds ahead — about a quarter mile at highway speed — and check mirrors regularly.
Following distance: at least one second for every 10 feet of vehicle length below 40 mph, plus one more second above 40 mph.
Stopping distance: at 55 mph on dry pavement, a loaded truck needs well over 400 feet to stop, counting perception, reaction and braking distance — more with air brake lag.
Speed and curves: slow down before curves; large vehicles can roll over at posted advisory speeds.
Space overhead and below: know your vehicle's height; watch for low bridges and railroad crossings where a low trailer can get stuck.
Communicating: signal early, use hazard lights when stopped, and do not wave other drivers through.
Cargo: inspect cargo and securement within the first 50 miles, then every 150 miles or 3 hours, whichever comes first.

Key topics: downgrades, hazards and emergencies

Questions about mountain driving and emergencies are common. On a long downgrade, select a low gear before starting down and use engine braking. With air brakes, use the snub braking technique: once you reach your safe speed, brake firmly until you are about 5 mph below it, release, and repeat — rather than riding the brakes, which causes brake fade.

In an emergency, steering around a hazard is often safer than stopping, because a heavy vehicle needs so much distance to stop. Do not apply the brakes while turning sharply. If a skid begins, release the brakes or the accelerator and steer to straighten out. Vehicles with ABS should be braked normally; ABS helps keep control but does not shorten stopping distance by itself.

After stopping on the road or shoulder, turn on your hazard lights and place warning devices within 10 minutes: on a two-lane road, one within 10 feet of the rear on the traffic side, one about 100 feet behind and one about 100 feet ahead; on a divided highway, at 10, 100 and 200 feet behind. Move them back as far as 500 feet if a hill or curve hides your vehicle.

Hours of service, alcohol and disqualifications

FMCSA's hours-of-service rules prevent fatigue. Property-carrying drivers may drive up to 11 hours after 10 consecutive hours off duty, may not drive beyond the 14th hour after coming on duty, must take a 30-minute break after 8 cumulative hours of driving, and may not drive after 60 or 70 on-duty hours in 7 or 8 consecutive days; a 34-hour restart resets that limit. Passenger-carrying drivers have a 10-hour driving limit and a 15-hour on-duty limit.

The BAC limit in a commercial vehicle is 0.04%. Drivers may not use alcohol within 4 hours before going on duty, and any detectable alcohol puts a driver out of service for 24 hours. Employers must check FMCSA's Drug and Alcohol Clearinghouse. Many offenses also cost CDL holders their commercial privileges even when committed in a personal car:

Common CDL disqualifications (federal minimums)
Offense	First offense	Second offense
DUI, refusing an alcohol test, leaving the scene of a crash	1 year (3 years if hauling hazmat)	Lifetime
Two serious traffic violations in 3 years (such as speeding 15+ mph over, reckless driving, texting)	60 days	120 days for a third
Railroad-highway grade crossing violations	60 days	120 days (1 year for a third)
Using a vehicle in a felony involving controlled substances	Lifetime, no reinstatement	—

Language, test day and retakes

Language policies for CDL knowledge tests vary by state and changed in several states in 2025: some still offer the tests in Spanish or other languages, while others give them only in English. Whatever language you test in, you must meet the federal English proficiency requirement to operate a commercial vehicle, so learn the technical vocabulary in English as you study.

On test day, bring your driver's license, your medical examiner's certificate, identity and residency documents your state requires, and the fee. Many states give the knowledge tests on a computer and score each test separately, so you can pass general knowledge and retake only the test you missed. Retake waiting periods and fees vary; ask before you leave.

How to study for the CDL general knowledge test

Download your state's current CDL manual and read the general knowledge section carefully, then the sections for air brakes, combination vehicles and any endorsements you want. Make a sheet of the numbers: tread depths, following-distance formula, warning-device distances, inspection intervals, hours-of-service limits and the 0.04% BAC limit.

Then practice. Take our practice tests by topic, review every explanation, and move to timed full mock exams once you score above 90% on each topic. Basic road rules still matter, so review signs and right-of-way with our road signs guide. Combine study with your ELDT course: the theory portion covers the same material and will make the knowledge test much easier.

How to get a commercial learner's permit (CLP)

Check eligibility You need a valid driver's license and must be at least 18 to drive within your state or 21 to drive interstate or haul placarded hazardous materials.
Pass the DOT medical exam Get a medical examiner's certificate from a certified examiner listed on the FMCSA National Registry.
Study the state CDL manual Focus on the general knowledge section plus the sections for your class and endorsements.
Pass the knowledge tests Take the general knowledge test and any required tests such as air brakes and combination vehicles.
Receive your CLP and complete training Hold the CLP at least 14 days and complete required Entry-Level Driver Training before the skills test.
Pass the CDL skills test Pass the vehicle inspection, basic control and on-road tests in a vehicle of the class you want.

CDL general knowledge test FAQ

How many questions are on the CDL general knowledge test?

In most states, 50 multiple-choice questions, and you need 80% (40 correct) to pass. Check your state's CDL manual for its exact format.

Is the CDL general knowledge test hard?

It is longer and more technical than a car permit test, with many numbers to remember. Most people pass on the first try if they read the CDL manual and practice until they score above 90%.

How long do I have to hold a CLP before the skills test?

At least 14 days under federal rules. A CLP is valid for no more than one year, and you must also complete required Entry-Level Driver Training before the skills test.

Can I get a CDL at 18?

Yes, for driving within your state (intrastate). You must be 21 to drive across state lines or haul placarded hazardous materials.

What is ELDT?

Entry-Level Driver Training is federally required training, in effect since February 7, 2022, for first-time Class A and B applicants, class upgrades and the P, S and H endorsements. It must come from a provider on FMCSA's Training Provider Registry.

What is the BAC limit for CDL drivers?

0.04% in a commercial vehicle. Any detectable alcohol takes the driver out of service for 24 hours, and a DUI in any vehicle can disqualify a CDL holder for a year or more.

Can I take the CDL test in another language?

Some states offer CDL knowledge tests in other languages and others give them only in English. Federal rules require commercial drivers to read and speak English sufficiently, so check your state's current policy.