CDL General Knowledge Practice Test 2026 — 154 Free Questions + Cheat Sheet
The CDL General Knowledge test is the first and hardest part of getting your commercial driver's license. With a national first-attempt failure rate near 40%, most applicants fail because they memorize facts without understanding why. This page gives you 154 FMCSA-verified practice questions plus a printable cheat sheet of the 25 non-negotiable numbers — air pressures, following distances, tread depths, cargo securement rules — that determine pass or fail.
Key Facts
- •The CDL General Knowledge test is 50 questions drawn from a pool, administered by your state DMV. Passing score is 80% (40/50). Time limit: typically 60 minutes.
- •After passing General Knowledge, you must pass endorsement tests for any specialized driving: Air Brakes (required for vehicles with air brakes), Combination Vehicles (required for tractor-trailers), Tanker, Doubles/Triples, Hazmat, Passenger, School Bus.
- •Air Brakes test: 25 questions, 80% passing. Tests knowledge of air brake system components, operation, inspection, and stopping distance. This is the most commonly failed endorsement.
- •Combination Vehicles test: 20 questions, 80% passing. Tests coupling/uncoupling, vehicle inspection for combination units, and stability factors (rollover, jackknife prevention).
- •CDL medical requirements: DOT physical exam by FMCSA-certified medical examiner. Valid for up to 24 months. Must submit Medical Examiner's Certificate (MEC) to state DMV.
- •Entry-Level Driver Training (ELDT) rule: since February 7, 2022, all new CDL applicants must complete FMCSA-registered theory and behind-the-wheel training before taking the skills test.
- •Our 154 questions are verified against the official CDL Driver's Manual (FMCSA Model Manual) and organized by knowledge node: safety, inspection, air brakes, vehicle control, cargo.
- •CDL permits are valid for 180 days to 1 year (varies by state). You must hold the permit for at least 14 days before taking the skills test.
- •Average self-study time to pass General Knowledge: 20-30 hours. Add 10-15 hours for Air Brakes and 8-12 hours for Combination Vehicles if you need those endorsements.
- •The CDL Driver's Manual is free from every state DMV website and from FMCSA. The manual IS the test content — questions are written directly from it.
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154 FMCSA-verified CDL questions. Air Brakes, Combination Vehicles, Cargo, Hazmat, Tanker endorsements. Mock exam mode with 60-minute timer.
Start FREE CDL Practice →The CDL Cheat Sheet: 25 Numbers You Must Memorize
The CDL test is number-heavy. Air pressures, distances, weights, tread depths — if it has a number, it's on the test. Print this section and put it on your fridge.
CDL General Knowledge — Key Numbers Cheat Sheet
| Category | Number | What It Means |
|---|---|---|
| Air Brakes | 60-120 psi | Normal operating range for air brake systems |
| Air Brakes | 60 psi | Low air pressure warning light/buzzer must activate before this |
| Air Brakes | 20-45 psi | Spring brakes (emergency/parking) typically apply at this pressure |
| Air Brakes | 3 psi | Max air loss in 1 minute with engine off, brakes released (static test) |
| Air Brakes | 4 psi | Max air loss in 1 minute with engine off, brakes applied (applied test) |
| Air Brakes | 100 psi | Compressor should build pressure from 85 to 100 psi in <45 seconds |
| Following Distance | 4 seconds | Minimum following distance for vehicles under 40 ft at ≤40 mph |
| Following Distance | 5-6 seconds | Minimum following distance for vehicles over 40 ft at ≤40 mph |
| Following Distance | +1 second | Add for each adverse condition (rain, snow, night, heavy traffic) |
| Tires | 4/32 inch | Minimum tread depth for front/steering tires |
| Tires | 2/32 inch | Minimum tread depth for all other tires |
| Stopping | 250-300 ft | Typical stopping distance for loaded tractor-trailer at 55 mph dry road |
| Weight | 80,000 lbs | Federal maximum gross vehicle weight (GVW) without special permit |
| Weight | 20,000 lbs | Federal maximum single-axle weight limit |
| Weight | 34,000 lbs | Federal maximum tandem-axle weight limit |
| Cargo | 10% | Minimum cargo weight on steering axle for proper control |
| Bridge Formula | Max = 500 [LN/(N-1) + 12N + 36] | Federal Bridge Formula — limits weight based on axle count and spacing |
| Hazmat | 1.0 | Placard required if any amount of Table 1 hazmat (explosives, poison gas, etc.) |
| Hazmat | 1,001 lbs | Placard required for Table 2 hazmat if aggregate exceeds this weight |
| Alcohol | 0.04% | CDL DUI limit (half the standard 0.08% — CDL drivers held to stricter standard) |
| Railroad | 15-50 ft | Stop distance before railroad crossing (15 ft min, 50 ft max) |
| Railroad | No shift | Never shift gears while crossing railroad tracks |
| Inspection | 3 points | Minimum tread depth on steering tires is measured in major grooves at 3 points |
| Lights | 500 ft | Headlights required when visibility is less than 500 ft |
| Fire Ext. | 5 BC | Minimum fire extinguisher rating for commercial vehicles carrying hazmat |
Master CDL Air Brakes — Most Failed Endorsement
50+ air brake-specific questions. Dual circuit systems, spring brakes, static/applied leakage tests, emergency stops. Detailed FMCSA manual references.
Practice Air Brakes Now →CDL Endorsements: Complete Guide
CDL Endorsement Requirements
| Endorsement | Code | Test Qs | Passing | Required For | Key Topics |
|---|---|---|---|---|---|
| Air Brakes | L | 25 | 80% | Any vehicle with air brakes | Air system components, inspection, stopping distance, brake lag |
| Combination | None | 20 | 80% | Tractor-trailer combinations | Coupling/uncoupling, jackknife prevention, trailer inspection |
| Tanker | N | 20 | 80% | Liquid/dry bulk tanks ≥1,000 gal | Slosh/ surge effects, liquid weight distribution, outage/ullage |
| Doubles/Triples | T | 20 | 80% | Pulling 2-3 trailers | Coupling, converter dolly, rearward amplification (crack-the-whip) |
| Hazmat | H | 30 | 80% | Transporting hazardous materials | Placarding, classes, shipping papers, emergency response, security |
| Passenger | P | 20 | 80% | Vehicles designed for 16+ passengers | Loading, emergency exits, railroad crossings, passenger management |
| School Bus | S | 25 | 80% | School buses | Loading/unloading, student management, emergency evacuation, crossing arms |
Hazmat Endorsement: Worth the Effort
Hazmat-endorsed CDL drivers earn $10,000-20,000 more per year than non-hazmat drivers. The endorsement requires a TSA background check (fingerprints, ~$86 fee) in addition to the written test. Processing takes 30-60 days. The test covers hazard classes (1-9), placarding thresholds (Table 1 vs Table 2), shipping papers location and content, emergency response guidebook (ERG) usage, and security requirements (route restrictions, attendance rules for certain hazmat loads).
CDL Exam Structure: General Knowledge + Skills Test
CDL Testing Path
- 1Step 1: Get the CDL Manual
Download the free CDL Driver's Manual from your state DMV website or FMCSA. This is your primary study material — every question comes from this book. Read the General Knowledge section (Sections 1-3) cover to cover once before taking any practice tests.
- 2Step 2: DOT Medical Exam
Schedule a DOT physical with an FMCSA-certified medical examiner. You must pass this before applying for a permit. Bring the Medical Examination Report form. The examiner checks vision (20/40, 70° field), hearing (forced whisper at 5 ft), blood pressure, and general health. Valid for up to 24 months.
- 3Step 3: ELDT Theory Training
Since February 2022, all new CDL applicants must complete FMCSA-registered Entry-Level Driver Training. This includes ~30 hours of theory (classroom or online) covering basic operation, safe operating procedures, advanced operating practices, vehicle systems, and non-driving activities. Cost: varies by provider.
- 4Step 4: Written Tests at DMV
Go to your state DMV and take the written tests: (1) General Knowledge — 50 questions, 60 minutes, 80% passing. (2) Air Brakes — 25 questions (if applicable). (3) Combination Vehicles — 20 questions (if applicable). (4) Any endorsement tests you need. Pass all written tests to get your Commercial Learner's Permit (CLP).
- 5Step 5: Behind-the-Wheel Training
Complete ELDT behind-the-wheel training: ~30 hours including range (maneuvers) and road (public driving). This must be done with a registered training provider. Your CLP must be at least 14 days old before you can take the skills test.
- 6Step 6: CDL Skills Test
Three-part skills test at DMV or approved third-party tester: (a) Pre-trip Vehicle Inspection — identify and explain parts you're checking, (b) Basic Vehicle Control — maneuvers (straight line backing, offset backing, parallel parking), (c) Road Test — on-road driving, shifting, turning, intersections, railroad crossings, highway driving.
Test Your CDL Knowledge Now
154 free questions across General Knowledge, Air Brakes, Combination Vehicles, Cargo, Hazmat, and Tanker. Instant scoring with FMCSA manual references.
Start FREE CDL Practice →Official Sources
Official CDL Exam Sources
- FMCSA CDL Driver's Manual (Model) — The model CDL manual from FMCSA — the basis for all state CDL tests
- FMCSA Entry-Level Driver Training Rule — ELDT requirements effective February 7, 2022 — mandatory for all new CDL applicants
- Federal Motor Carrier Safety Regulations (FMCSR) — 49 CFR Parts 380-399 — hours of service, vehicle inspection, cargo securement, hazmat rules
- 49 CFR Part 383 — CDL Standards — Federal CDL standards — knowledge and skills test requirements, endorsements, disqualifications
154 Free CDL Questions — Start Now
General Knowledge + Air Brakes + Combination + Cargo + Hazmat + Tanker. FMCSA-verified. Mock exam mode with timer. 100% free, no signup.
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