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The CDL exam is really several tests: a written knowledge test for your Commercial Learner's Permit, endorsement knowledge tests, a pre-trip inspection, basic control skills, and a road test. This page focuses on the written portion — every knowledge test you may need to pass, in the order most people take them.
What is the CDL written test?
The CDL written test is the knowledge portion of the CDL exam. It's a series of multiple-choice tests based on the FMCSA regulations and your state's CDL manual. You pass each with an 80% score. Passing General Knowledge (plus Air Brakes and Combination Vehicles for Class A) earns your Commercial Learner's Permit — the CLP you drive on before taking the road test.
General Knowledge
Required for every CDL applicant. Covers vehicle inspection, basic control, shifting, backing, seeing, communicating, space management, night driving, extreme weather, hazards, skid recovery, accident procedures, and cargo basics. Usually 50 questions.
Air Brakes
Required for any CDL vehicle equipped with air brakes. Covers dual air systems, spring parking brakes, the seven-step brake check, low-air warning, static leakage, and applied leakage tests. If you skip this test your license will be restricted to non-air-brake vehicles.
Combination Vehicles
Required for Class A (tractor-trailer). Coupling and uncoupling, off-tracking, rollover prevention, trailer brake operation, and inspecting the fifth wheel, kingpin, and landing gear.
HazMat (H) Endorsement
Required to haul placarded hazardous materials. Covers the hazardous materials table, shipping papers, placarding, loading and unloading, driving and parking rules, and emergency response. Also requires a TSA background check and ELDT theory.
Tanker (N) Endorsement
Required to haul liquid or gaseous bulk cargo. Focuses on liquid surge, high center of gravity, outage/expansion, baffled vs. smooth-bore tanks, and safe cornering speeds.
Passenger (P) Endorsement
For any vehicle designed to carry 16 or more people, including the driver. Pre-trip specific to buses, standee lines, prohibited practices, emergency exits, and railroad crossings.
School Bus (S) Endorsement
Adds school-bus-specific rules on top of P: student loading and unloading, danger zones, flashing lights and stop arm, railroad crossings, and post-trip child checks. Requires ELDT before the skills test.
Doubles & Triples (T) Endorsement
Required to pull two or three trailers. Covers coupling and uncoupling multiple trailers, checking the converter dolly, and managing extreme rearward amplification (the 'crack the whip' effect).
ELDT (Entry-Level Driver Training)
Since Feb 7, 2022, new CDL applicants must complete FMCSA-approved theory and behind-the-wheel training from a provider on the FMCSA Training Provider Registry before upgrading from CLP to CDL, or before adding a Passenger, School Bus, or HazMat endorsement.
Medical Card (DOT Physical)
Interstate CDL drivers need a current Medical Examiner's Certificate from a certified examiner on the National Registry. Intrastate rules vary by state. The card is typically valid for up to 24 months.
The Permit (CLP) process
Verify you meet the age and residency rules for your state, gather the required documents (proof of identity, SSN, residency, and medical certificate for interstate), pass the knowledge tests, then apply for the CLP. Most states require holding the CLP for at least 14 days before the skills test.
How to study for the CDL written test
Read the study guide for one topic, take the matching practice test, review every wrong answer with its explanation, and repeat until you can consistently hit 90% in exam mode. Short daily sessions beat long weekend cramming.
Common mistakes on the CDL written test
Skipping the state manual, memorizing questions instead of understanding the rule, ignoring Air Brakes because 'I'll add it later' (you'll be restricted), and not practicing under real exam-mode conditions with an 80% passing bar.
Practice tests
Free CDLTest360 practice tests mirror the actual DMV format: multiple choice, 80% to pass, instant explanations, and mistake tracking so you focus on what you keep getting wrong.
FAQs
- What is the CDL written test?
- The CDL written test is a series of DMV-administered knowledge exams — General Knowledge plus any endorsement or vehicle-specific tests (Air Brakes, Combination Vehicles, HazMat, Passenger, School Bus, Tanker, Doubles/Triples). Passing them earns you a Commercial Learner's Permit (CLP), which you need before the skills (road) test.
- How many questions are on the CDL written test?
- General Knowledge is 50 questions in most states. Endorsement tests are typically 20–30 questions each. Every knowledge test uses an 80% passing score.
- How long does it take to study for the CDL written test?
- Most drivers are ready in 2–4 weeks of consistent study. Read the study guide for each topic, then take practice tests until you can score 90% or better on exam mode.
- Do I have to take all the endorsement tests?
- No — only the ones you want on your license. General Knowledge is required for every CDL. Add Air Brakes if the vehicle has air brakes, Combination Vehicles for Class A, and any endorsements (H, P, S, T, N, X) you plan to use.
- Can I take the CDL written test online?
- No. Every state requires the knowledge test to be taken in person at a DMV or licensed testing center. Practice tests like CDLTest360 are for preparation, not for the actual exam.
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