The Short Answer
The general knowledge test is the written exam you pass to get a commercial learner's permit (CLP) — the first step toward a Class A, B or C CDL. Federal law fixes the pass mark: you must answer at least 80% of the questions correctly (49 CFR 383.135). It does not fix the length; each state builds its test from a federally approved question pool, and 50 questions is the most common format, which means you can miss 10. The questions come from the state's CDL manual, and every state's manual is built on the same national model — so the content is close to identical from Maine to California.
| Item | Rule | Source |
|---|---|---|
| Pass mark | 80% on every knowledge test (general and each endorsement) | 49 CFR 383.135 |
| Number of questions | Set by your state — commonly 50 for general knowledge | State CDL manual |
| Minimum age for a CLP | 18 (21 to drive across state lines) | 49 CFR 383.25, 391.11 |
| CLP validity | No more than one year from first issue without retesting | 49 CFR 383.25(c) |
| Wait before the skills test | At least 14 days after the CLP is first issued | 49 CFR 383.25(e) |
| Entry-level training | Required before the skills test for a first Class A or B CDL, a B-to-A upgrade, or a first S, P or H endorsement | 49 CFR Part 380 (since 7 Feb 2022) |
Want to see the style of question first? Our free CDL general knowledge questions show the answer, the explanation and the manual section for each one, and the 20-question practice quiz scores you at the real 80% bar.
What the General Knowledge Test Covers
State CDL manuals follow the model manual published by AAMVA, the association of state licensing agencies. The general knowledge test draws on three of its sections, and the weight falls heavily on the second:
- Section 1 — Introduction: license classes, which vehicles need a CDL, disqualifications, and the rules on alcohol, drugs and serious traffic violations.
- Section 2 — Driving Safely: the bulk of the test. Vehicle inspection, basic control, shifting, seeing and communicating, space management, speed and stopping distance, hazards and distraction, night, winter, hot-weather and mountain driving, railroad crossings, skid control, emergencies, crashes and fires, and hazardous-materials basics.
- Section 3 — Transporting Cargo Safely: inspecting cargo, weight and balance, securing loads, and cargo that needs special care.
Everyone takes this test. Which other tests you take depends on the license class and what you will haul:
| Knowledge test | Who needs it |
|---|---|
| General knowledge | Every CDL applicant |
| Air brakes | Anyone driving a vehicle with air brakes; failing it puts an air-brake restriction on the license |
| Combination vehicles | Class A (tractor-trailers) |
| Passenger (P) | Buses carrying 16 or more people including the driver |
| School bus (S) | School bus drivers — taken with the passenger test |
| Tank vehicle (N) | Liquid or gas in bulk tanks |
| Doubles/triples (T) | Pulling two or three trailers |
| Hazardous materials (H) | Placarded hazmat loads; also requires a TSA security threat assessment |
The Numbers That Decide Most Failures
Judgement questions — slow down in fog, look further ahead at night — rarely sink anyone. Specific numbers do, because they cannot be reasoned out at the screen. These come from the model manual and the federal rules it summarises:
| Rule | Number |
|---|---|
| Following distance under 40 mph | 1 second for every 10 feet of vehicle length (40-ft truck = 4 seconds) |
| Following distance over 40 mph | Add 1 more second |
| How far ahead to look | 12–15 seconds — about a quarter of a mile at highway speed |
| Total stopping distance | Perception + reaction + braking distance; about 419 feet from 55 mph |
| Doubling speed (20 → 40 mph) | Braking distance and impact become 4 times greater |
| Minimum tire tread | 4/32 inch on front (steering) tires, 2/32 inch on all others |
| Warning triangles | Within 10 minutes of stopping: 10 feet, 100 feet and 100 feet (one ahead, two behind on a two-way road) |
| Railroad crossings (buses, hazmat) | Stop no closer than 15 feet and within 50 feet of the tracks |
| Cargo checks | Within the first 50 miles, then every 3 hours or 150 miles and at every change of duty status |
| Alcohol before driving | None within 4 hours of going on duty |
| Any detectable alcohol on duty | Out of service for 24 hours |
| Alcohol concentration limit in a CMV | 0.04 — half the usual car limit |
| First DUI or 0.04+ in a CMV | 1-year disqualification (3 years if hauling placarded hazmat); a second offense is disqualification for life |
If you already drive a car, notice the pattern: the CDL versions are stricter than the car rules you know. The alcohol limit is half; following distances are measured in seconds per 10 feet of truck, not a flat three seconds; and a conviction in your personal car can still cost you your CDL.
From Knowledge Test to CDL: The Order of Steps
- Get a DOT medical certificate if you will drive interstate — most states ask for it (or your self-certification) when you apply for the CLP.
- Pass the knowledge tests for your class and endorsements at the state licensing office. The CLP is issued on the spot or by mail.
- Complete entry-level driver training (ELDT) with a provider listed on FMCSA's Training Provider Registry if you are getting your first Class A or B CDL, upgrading from B to A, or adding S, P or H for the first time. The provider reports completion to the registry; the state checks it before your skills test. Federal rules do not require the theory part before the permit, but many schools schedule it that way.
- Hold the CLP for at least 14 days and practise with a qualified CDL holder beside you.
- Pass the three-part skills test — vehicle inspection, basic control, and the road test — in a vehicle of the class you are licensing for.
How to Prepare in Two Weeks
- Read Sections 1–3 of your state's CDL manual once, straight through. It is the source of every question. Mark every number as you go.
- Make a one-page number sheet from the table above plus anything your state adds (fines, state-specific weight limits), and review it daily.
- Learn the pre-trip inspection as a fixed sequence. Inspection questions test order and specific defects — tire tread, leaks, loose lug nuts, cracked rims — and a memorised walk-around answers most of them.
- Practise at the real bar. Take full sets and do not book the test until you score 90% or better twice in a row; the extra margin absorbs the handful of unfamiliar questions every real test has. Our CDL practice test explains each answer and cites the manual section.
- Study the endorsement sections you need in the second week, one per day, with air brakes first for anyone driving a truck with air brakes.
New to written driving tests altogether? The rules car drivers most often get wrong are a useful warm-up — several reappear on the CDL test with stricter numbers.
Frequently Asked Questions
How many questions are on the CDL general knowledge test?
It depends on the state. Federal rules require a pass mark of 80% but let each state set the length; 50 questions is the most common, which allows 10 wrong answers. Check your state's CDL manual or licensing agency for the exact number.
What score do I need to pass the CDL permit test?
At least 80% on each knowledge test, under 49 CFR 383.135. The general knowledge test and each endorsement test are scored separately.
How long is a CDL learner's permit valid?
No more than one year from the date it was first issued. States may issue it for a shorter term and renew it, but not beyond one year in total without retaking the knowledge tests.
How soon after getting my CLP can I take the skills test?
Not in the first 14 days after the permit is issued. First-time Class A or B applicants must also have completed entry-level driver training with a registered provider.
How old do you have to be to get a CDL?
18 to hold a CLP and drive commercially within your state; 21 to drive a commercial vehicle across state lines. Some states set higher ages for particular endorsements, so check your state manual.
Is the CDL knowledge test the same in every state?
Very close. Every state builds its tests from a federally approved question pool and its manual from the same national model, so the topics and most numbers match. States differ in length, fees, languages offered and a few state-specific rules.
Sources
- 49 CFR Part 383 — §383.25 (CLP: age 18, one-year validity, 14-day wait), §383.51 (disqualifications), §383.135 (80% pass mark).
- 49 CFR Part 392 — §392.5 (4-hour alcohol rule, 24-hour out-of-service), §392.9 (cargo inspection), §392.10 (railroad crossings), §392.22 (warning devices).
- FMCSA — Entry-Level Driver Training — who must complete ELDT and the Training Provider Registry.
- AAMVA Model Commercial Driver's License Manual — Sections 1–3 (following distance, stopping distance, tread depth, look-ahead distance), the basis of every state's CDL manual.
