CDL General Knowledge Test: 50 Questions, 80% to Pass (2026)

The CDL General Knowledge test is the one exam every commercial driver applicant has to pass, whatever class of license or endorsements they are going for. It is 50 multiple-choice questions and most states require 80% to pass — meaning you can miss only 10. This guide covers what the test asks, which sections cause the most failures, and how to prepare for them specifically.

What the CDL General Knowledge Test Covers

The questions come from your state’s CDL manual, which is built on the Federal Motor Carrier Safety Regulations. The material breaks into these areas:

• Vehicle inspection — the pre-trip sequence, what to check in the engine compartment, cab, and exterior, and what a Driver Vehicle Inspection Report is for
• Basic control and shifting — backing, the clutch brake, double clutching, and why you never shift while turning or crossing tracks
• Space management — following distance, the one-second-per-10-feet rule, and No-Zones
• Speed management — total stopping distance, brake lag, and why heavy vehicles need far more room
• Hazard perception and emergencies — skid recovery, tire blowouts, brake failure, and escape ramps
• Cargo securement — weight distribution, tie-down requirements, and axle weight versus GCWR
• Hours of Service — the 11-hour driving limit, 14-hour window, 30-minute break, and 60/70-hour rules
• Alcohol, drugs, and driver fitness — including the 0.04% commercial BAC limit

The Two Sections That Fail the Most People

If you only have limited study time, weight it toward these.

Air Brakes

Air brakes are the single most commonly failed portion, and it is a numbers problem more than a concepts problem. The figures that come up repeatedly:

• Normal operating pressure is typically 100 to 125 psi
• The low air pressure warning activates around 60 psi
• Spring brakes apply automatically between roughly 20 and 45 psi
• Air brakes add brake lag distance to total stopping distance, which hydraulic brakes do not have

Note that if your vehicle has air brakes you must also pass a separate 25-question Air Brakes test, again at 80%. A failure there restricts your license even if you passed General Knowledge.

Combination Vehicles

The second-hardest section. Expect questions on off-tracking (why trailer wheels cut a tighter path in a turn), fifth-wheel coupling and the tug test, what the emergency air line does when pressure is lost, and jackknifing — which is most often caused by locked trailer wheels on a lightly loaded trailer.

How the Scoring Actually Works

Each knowledge test is scored on its own. A strong score on General Knowledge does not offset a weak score on Air Brakes; you have to clear 80% on each test you take. Requirements and retake rules are set state by state, so confirm the specifics with your own state’s licensing agency before test day.

A Study Approach That Works

Read the manual chapter, then immediately answer questions on that chapter rather than reading the whole book first. Recall is what the test measures, and re-reading creates a false sense of familiarity that does not survive exam conditions.

Once you are consistently above 85% on practice sets, shift to the sections that fail people — air brakes numbers and combination vehicle handling — and drill those until the figures are automatic.

Our CDL Practice Tests course has 300 questions across 12 full practice tests, including two dedicated specifically to air brakes and combination vehicles. Every question carries an explanation of why the answer is right. There are also free CDL flashcards with a study mode that brings back the cards you miss more often, and a free preview quiz with no signup.

Frequently Asked Questions

How many questions is the CDL General Knowledge test?

50 multiple-choice questions. Most states require 80% to pass, which means 40 correct.

What is the hardest part of the CDL written test?

Air Brakes is widely reported as the most failed section, with Combination Vehicles second. Both are number-heavy and reward memorization of specific pressure and procedure details.

Do I have to take the Air Brakes test?

Only if the vehicle you will drive has air brakes. If you skip it or fail it, your license carries a restriction barring you from operating air-brake-equipped vehicles.

How long should I study for the CDL General Knowledge test?

It varies by background, but most candidates who pass first time report working through several hundred practice questions rather than only reading the manual.