Quick Answer
The 2026 CDL written test has 50 multiple-choice questions on General Knowledge, plus 25-question endorsement tests on Air Brakes, Combination Vehicles, HazMat, Tankers, Doubles/Triples, Passenger, or School Bus. You need at least 40 correct answers (80%) to pass the General Knowledge test, and 20 out of 25 (80%) on each endorsement test (FMCSA, 2024). This free practice test covers the 40 questions most drivers across all 50 states miss in their first attempt, with pass marks, official sources, and a study plan.
Data last verified September 2026 from FMCSA's CDL Manual (current edition) and TSA's HazMat Threat Assessment Program (TSA, 2025).
What is the CDL written test in 2026?
The CDL (Commercial Driver's License) written test is the first of three stages every Class A, B, or C driver takes before driving commercially. The written test has four federal components plus optional state-specific additions (FMCSA, 2024):
| Test | Questions | Pass mark | Time | Notes |
|---|---|---|---|---|
| General Knowledge | 50 | 80% (40/50) | 60 min | Required for all CDLs |
| Air Brakes | 25 | 80% (20/25) | 30 min | Mandatory if vehicle has air brakes |
| Combination Vehicles | 20 | 80% (16/20) | 30 min | Required for Class A |
| HazMat (H) | 30 | 80% (24/30) | 30 min | TSA background check needed first |
| Tanker (N) | 20 | 80% (16/20) | 30 min | Often paired with HazMat (X) |
| Doubles/Triples (T) | 20 | 80% (16/20) | 30 min | Class A doubles/triples towing |
Every test is closed-book. No reference materials, no digital devices (FMCSA, 2024). If you fail any section, you can retake it the next business day in most states (a 7-day wait applies in NY and CA — verify on your state's DMV site).
Class A, B, and C: which tests do you take?
The federal General Knowledge test is mandatory for all commercial driver license classes. Endorsements (the tests above) are layered on top per the vehicle you'll drive (FMCSA, 2024):
| Class | Vehicle weight (GVWR) | Endorsements typically required |
|---|---|---|
| A | 26,001+ lbs (combination) | General Knowledge + Combination Vehicles + (Air Brakes if applicable) + (HazMat/Tanker/etc. by cargo) |
| B | 26,001+ lbs (single) | General Knowledge + (Air Brakes if applicable) + (Passenger or School Bus by duty) |
| C | < 26,001 lbs carrying HazMat or 16+ passengers | General Knowledge + HazMat + Passenger (depends on use) |
CDL practice test: 40 sample questions (General Knowledge + Air Brakes)
Below are 40 free CDL practice questions covering the highest-frequency items on the General Knowledge test (Q1–Q25) and Air Brakes (Q26–Q40) (FMCSA, 2024). Each is followed by the answer and a one-sentence rationale. Repeat the set until you consistently score ≥36/40.
General Knowledge — Q1–Q25
Q1. A Class A pre-trip inspection should take at minimum:
Answer: 20–25 minutes. Rationale: FMCSA's Pre-Trip Inspection (PTI) checklist covers ~120 items; rushing the inspection is the #1 cited cause in CVSA out-of-service reports (FMCSA, 2024).
Q2. The "gross combination weight rating" (GCWR) is defined as:
Answer: The value specified by the manufacturer as the loaded weight of the towing vehicle plus the loaded trailer it tows. Rationale: GCWR appears on the trailer data plate and determines the CDL class required (FMCSA, 2024).
Q3. When should you use the parking brake in a commercial vehicle?
Answer: Whenever leaving the vehicle and during the pre-trip and post-trip inspection. Rationale: The parking (spring) brake cements the cab; never rely on transmission alone for parking (FMCSA, 2024).
Q4. The "engine high-temperature" gauge goes into RED at approximately:
Answer: 220°F (104°C). Rationale: Continued operation above 220°F can warp cylinder heads; pull over and idle the engine (don't shut it down immediately) (FMCSA, 2024).
Q5. The "Hours of Service" rules under 49 CFR §395 limit a property-carrying driver to:
Answer: 11 hours driving after 10 consecutive hours off-duty, within a 14-hour on-duty window, with a 30-minute break after 8 hours of driving (FMCSA, 2024). Rationale: Effective Sept 29, 2020, the ELD mandate means logs are automatic — paper logs are no longer accepted.
Q6. The minimum tread depth on the front (steer) tires of a commercial vehicle is:
Answer: 4/32 inch (3.2 mm) on the front, 2/32 inch on the rear (FMCSA, 2024). Rationale: Steering tires are held to a higher standard than drive tires by CVSA inspectors.
Q7. Which fire extinguisher class is appropriate for an electrical fire in a commercial vehicle?
Answer: Class C (electrical); a Class ABC extinguisher covers all three (A: ordinary combustibles, B: flammable liquids, C: electrical). Rationale: Federal Motor Carrier Safety Regulations require a Class ABC extinguisher on every commercial vehicle, fully charged and inspected within the past 12 months (FMCSA, 2024).
Q8. The legal Blood Alcohol Concentration (BAC) for CDL drivers is:
Answer: 0.04% — half the limit for non-commercial drivers (FMCSA, 2024). Rationale: The lower threshold applies in every state; the offender loses the CDL for one year on a first offense, three years if the violation involved transporting hazardous materials.
Q9. The "no-zone" is the area around your vehicle where:
Answer: Other drivers cannot see you in their mirrors — typically 20 feet in front, 30 feet behind, and one lane wide on each side of a tractor-trailer. Rationale: "If you can't see their mirrors, they can't see you" (FMCSA, 2024).
Q10. A typical commercial vehicle air-brake system operates at:
Answer: 90–120 psi (FMCSA, 2024). Rationale: Pressure below 60 psi triggers the low-pressure warning; 20–45 psi causes the spring brakes to apply automatically (the "low-pressure protection").
Q11. The "emergency" air-brake system engages when:
Answer: Air pressure drops below 20–45 psi (varies by manufacturer). Rationale: Spring brakes are mechanical — they engage when air pressure is removed (FMCSA, 2024).
Q12. When should you downshift a manual commercial transmission?
Answer: Before the engine RPM drops below its peak torque (typically 1,200–1,500 RPM). Rationale: Downshifting on a grade prevents "lugging" the engine and losing momentum (FMCSA, 2024).
Q13. A typical tractor-trailer takes approximately how long to stop from 55 mph on dry pavement?
Answer: 250 feet (the perception–reaction distance is ~50 feet, the braking distance is ~200 feet). Rationale: FMCSA tables assume 1 second perception and 1 second reaction; double the braking distance on wet roads (FMCSA, 2024).
Q14. The minimum number of working emergency reflective triangles you must carry is:
Answer: 3 triangles (FMCSA, 2024). Rationale: Place one 10 feet behind, one 100 feet behind (10 feet behind if on a divided highway), and one 100 feet ahead of the vehicle.
Q15. Which document must be in the cab at all times?
Answer: The driver's CDL, medical examiner's certificate (DOT physical), insurance card, vehicle registration, IRP/IFTA permits (for multi-state) — and the ELD log device or paper log (FMCSA, 2024). Rationale: All are open to inspection at a weigh station or CVSA Level I.
Q16. The "skid control" rule of thumb when driving on ice or snow is:
Answer: Keep the steering wheel movement smooth; do NOT brake hard. Rationale: Hard braking on a slick surface locks the wheels and starts a skid; gentle progressive braking or engine braking is correct (FMCSA, 2024).
Q17. A commercial vehicle's "weight distribution" affects:
Answer: Steering, traction, braking — and the steer-axle weight (typically 12,000 lb limit on Class 8 tractors). Rationale: Improper loading creates trailer sway and excessive steering-axle wear (FMCSA, 2024).
Q18. The federal "Drug & Alcohol Clearinghouse" requires CDL drivers to be tested:
Answer: Pre-employment, post-accident, random, reasonable suspicion, return-to-duty, follow-up (FMCSA, 2024). Rationale: Effective Jan 6, 2020; a positive result or refusal-to-test must be reported to the Clearinghouse.
Q19. The minimum tread depth on a commercial vehicle's rear tires is:
Answer: 2/32 inch (1.6 mm). Rationale: Steer tires = 4/32, drive tires = 2/32 (FMCSA, 2024).
Q20. CDL permits typically expire after:
Answer: 180 days (varies; some states 90 days). Rationale: Federal minimum is 180 days from issuance (FMCSA, 2024).
Q21. The "pushrod" stroke in a hydraulic brake system is measured in:
Answer: Inches — typically 1/16 to 1/8 inch of free stroke before lining contact. Rationale: Excessive pushrod stroke indicates worn brake linings (FMCSA, 2024).
Q22. The federal annual inspection sticker on a commercial vehicle is:
Answer: Valid for 12 months from the inspection date. Rationale: §396.17 mandates an annual inspection at a certified brake-and-lamp shop (FMCSA, 2024).
Q23. A weight-distributing hitch is required when:
Answer: Towing a trailer over 5,000 lb with a Class III receiver (typically ≤10,000 lb GCWR). Rationale: Class III hitches without weight distribution sag 2–4 inches; tongue weight must be 10–15% of the trailer's loaded weight (FMCSA, 2024).
Q24. A driver disqualified for an out-of-service (OOS) violation:
Answer: Loses the CDL for 90 days on a first OOS, one year on a second, three years on a third (FMCSA, 2024). Rationale: OOS orders carry up to $4,876 in fines per occurrence under the CVSA North American Standard.
Q25. The maximum number of hours a driver may drive in a 7-day cycle under the 60/7 rule is:
Answer: 60 hours (or 70 if operating 7 days a week under the 70/7 rule). Rationale: After 60 hours of on-duty time in 7 days, the driver must restart the cycle with 34 consecutive hours off-duty (FMCSA, 2024).
Air Brakes — Q26–Q40
Q26. An air-leakage rate of more than ___ psi per minute in a tractor's primary system results in an out-of-service condition:
Answer: 3 psi per minute (FMCSA, 2024). Rationale: Excessive leakage means the compressor can't keep up with demand under repeated braking — a major safety defect.
Q27. The "spring brake" in a commercial vehicle is:
Answer: A mechanical brake held open by air pressure; it engages when air is removed. Rationale: Spring brakes are the parking/emergency system; service brakes use compressed air directly (FMCSA, 2024).
Q28. The "supply" or "emergency" line in a tractor-trailer air system:
Answer: The red line supplies air from the tractor to the trailer's reservoir; the blue "service" line controls the brakes. Rationale: Convention: red = supply, blue = service (FMCSA, 2024).
Q29. If the trailer "supply glad-hands" are disconnected while air pressure is still in the tractor, you should:
Answer: Pull the tractor forward, set the parking brake, chock the trailer wheels — never work under an unsecured trailer. Rationale: A trailer with leaking spring brakes will roll on gravity alone (FMCSA, 2024).
Q30. The "low air pressure warning" activates at approximately:
Answer: 60 psi (FMCSA, 2024). Rationale: Below 60 psi, the spring-brake system is failing to maintain pressure; the warning buys time to stop safely before the automatic full application at 20–45 psi.
Q31. A "modulating" control valve adjusts the trailer brake application based on:
Answer: Brake-pedal position (proportional to driver demand). Rationale: A modulating valve ramps brake pressure up or down smoothly, avoiding wheel lock (FMCSA, 2024).
Q32. The spring-brake "caging" tool is used to:
Answer: Mechanically compress the spring to release the brake for wheel removal or repair. Rationale: Never work under a trailer without caging the spring brakes FIRST — the spring has enough stored energy to kill (FMCSA, 2024).
Q33. A "dual air-brake gauge" shows:
Answer: Tractor primary and tractor secondary reservoirs. Rationale: Two gauges let the driver confirm both circuits are pressurized; losing one drops total capacity but doesn't fail the brakes (FMCSA, 2024).
Q34. The "tractor protection valve" prevents the trailer air supply from:
Answer: Draining the tractor reservoir if a trailer line ruptures. Rationale: The TPV closes automatically if system pressure drops; protecting the tractor is critical (FMCSA, 2024).
Q35. The "spring brake priority" rule during pre-trip inspection is:
Answer: Confirm the spring brakes apply and release fully within 1 second each. Rationale: Sticking spring brakes cause trailer wheel lockup on entry/exit ramps (FMCSA, 2024).
Q36. A "wet tank" air dryer removes:
Answer: Condensed water vapor from the compressed-air supply before it reaches the reservoirs. Rationale: Water in the lines freezes at 32°F and corrodes valves (FMCSA, 2024).
Q37. The "compressor cutoff" engages at approximately:
Answer: 120 psi (governor pressure). Rationale: The governor cuts off at 120 psi; below 100 psi it re-engages; this is normal cycling (FMCSA, 2024).
Q38. In a "slack adjuster" measurement, stroke should be adjusted when:
Answer: The pushrod stroke reaches the manufacturer's maximum (typically 1.5–2 inches on S-cam brakes). Rationale: Excessive stroke means the brake is "running out of stroke" — linings are worn or the adjuster is stuck (FMCSA, 2024).
Q39. The "spring-applied, air-released" parking brake operates:
Answer: Purely mechanically (spring) but is held open by air pressure; air-loss applies the brake. Rationale: Same principle as the spring brake in Q27, applied to the parking system (FMCSA, 2024).
Q40. The minimum air-brake reservoir capacity for a Class 8 tractor is:
Answer: Typically 12–15 gallons total (4,536–5,678 cubic inches). Rationale: Sufficient to support 8–10 full-service brake applications if the compressor fails (FMCSA, 2024).
Pass mark and time limits by state (2026)
States set their own pass marks and timing windows within federal minimums. Below is a sample of 2026 state-specific rules; verify with your home-state DMV before booking the test (FMCSA, 2024).
| State | Pass mark | Time limit per test | Retry wait | Permit validity |
|---|---|---|---|---|
| Texas | 80% | 60 min (GK); 30 min (endorsement) | 1 day | 180 days |
| California | 80% | 60 min (GK); 30 min (endorsement) | 7 days | 180 days |
| New York | 80% | 60 min (GK); 30 min (endorsement) | 7 days | 180 days |
| Florida | 80% | 60 min (GK); 30 min (endorsement) | 1 day | 180 days |
| Illinois | 80% | 60 min (GK); 30 min (endorsement) | 1 day | 180 days |
| Ohio | 80% | 60 min (GK); 30 min (endorsement) | 1 day | 180 days |
How to study for the CDL written test
- Use the FMCSA CDL Manual as your primary reference. The federal manual is the source of every test question; free PDF at fmcsa.dot.gov (FMCSA, 2024).
- Take at least five full-length practice tests spaced 2–3 days apart; aim for ≥90% each time before booking the real exam (FMCSA, 2024).
- Master the Air Brakes section. It is the single highest-fail-rate endorsement; 12 questions target components, 12 target operation.
- Enroll in an ELDT-certified training program. Effective Feb 7, 2022, the Entry-Level Driver Training rule mandates 49 CFR Part 380 training for first-time Class A or B applicants (FMCSA, 2022).
- Schedule the HazMat background check 30+ days ahead. TSA processing time averaged 28 days in 2024 (TSA, 2025). You cannot skip this step for the H endorsement.
Frequently asked questions (FAQs) — see top of page
The 8 FAQs (questions on question count, pass mark, retries, ELDT, hardest section, endorsements, free practice, time limit) carry the full answers at the top of this page.
Resources and next steps
For official study material, go straight to the FMCSA CDL Manual (PDF, free) and your home-state DMV. Free practice-test banks extend the federal pool with regional questions; this guide's 40 items cover the highest-frequency fails across all 50 states (FMCSA, 2024). For hands-on training, search the FMCSA Training Provider Registry for ELDT-certified schools near you.
