CDL Written Test 2026: General Knowledge Test Guide, What to Study & How to Pass

The CDL written test — officially called the General Knowledge test — is the first milestone in the CDL licensing process. You need to pass it to get your Commercial Learner’s Permit, and without a CLP you can’t legally practice driving a commercial vehicle or take the skills test. A lot of drivers underestimate this test, assume it’s straightforward, and end up failing it the first time. Don’t be that person. Here’s exactly what to study and how to approach the exam.

What to Expect at the DMV

The General Knowledge test is administered at your state DMV, either on a computer terminal or paper, depending on the facility. Most states require a minimum score of 80% — meaning you can miss at most 20% of the questions. The test is typically 50 to 100 questions long, varying by state. You’ll find out your result immediately after finishing.

You can take additional knowledge tests at the same appointment if you want to earn endorsements (like Air Brakes or Combination Vehicles) at the same time you get your CLP. This is actually efficient — you’re already there, and passing them now means fewer visits later. If you fail a test section, most states require a waiting period before you can retake it — typically 1–2 weeks.

Questions are multiple-choice — usually 4 options. They’re drawn from a test bank based on your state’s CDL driver’s manual, which in turn follows the federal model developed by FMCSA. Every state’s CDL manual covers the same core content — the specific wording of questions varies but the underlying information is consistent.

The Core Topic Areas — What’s Actually on the Test

1. Basic Vehicle Operation and Control

This is the largest chunk of the General Knowledge test. It covers fundamental principles of commercial vehicle operation:

• Stopping distance: At 55 mph, a loaded tractor-trailer can take up to 450 feet to stop under ideal conditions — that’s the length of 1.5 football fields. The test asks about how speed, weight, and road conditions affect stopping distance. Doubling your speed quadruples your stopping distance — that relationship is frequently tested.
• Following distance: The standard is 1 second of following distance per 10 feet of vehicle length at speeds under 40 mph, plus 1 additional second for every 10 mph over 40 mph. For a typical 60-foot combination, that’s 6 seconds at highway speed — more in wet or slippery conditions.
• Shifting and gear selection: When to upshift, when to downshift, and why coasting in neutral downhill is both dangerous and prohibited. The test often asks about engine braking on downgrades.
• Backing: The G.O.A.L. principle (Get Out And Look), when to use a spotter, and why you always back to the driver’s side when possible.

2. Pre-Trip Inspection

The test covers what the pre-trip includes and why each component matters — not just a memorized list but understanding the purpose. Common test questions include minimum tire tread depth (4/32 inch for front steer axles, 2/32 inch for other positions), when to check fluids (engine off and on level ground), and what constitutes a “reportable defect” on a DVIR.

Knowing the pre-trip sequence also prepares you for the skills test. Our CDL pre-trip inspection guide walks through the full 7-step procedure you’ll need to demonstrate in the skills test.

3. Driving Safely

This section covers hazard recognition, space management, night driving, adverse conditions, and emergency situations. Key concepts the test hits frequently:

• Seeing: Eye lead time (looking 12–15 seconds ahead), systematic mirror checks every 5–8 seconds
• Night driving: Never overdrive your headlights — you must be able to stop within your sight distance. High beams give you about 500 feet; low beams about 250 feet. Your speed must reflect those ranges.
• Curves: Speed too high for a curve creates centrifugal force that can roll your vehicle or push you off the road. Slow down before the curve, don’t brake in it.
• Skids: A drive-wheel skid (from braking too hard on slippery roads) is corrected by releasing the brakes to let wheels regain traction, then reapplying gradually. A front-wheel skid (from too much speed in a turn) is corrected by slowing without turning more sharply.

4. Hazardous Conditions and Emergency Maneuvers

Test questions cover black ice (invisible on road but present when bridges are slippery and air temperature is near or below freezing), hydroplaning (reduced contact between tires and road when speed is too high on wet surfaces — occurs above approximately 35 mph on standing water), and what to do if your brakes fail going downhill (downshift, use escape ramp if available, use engine braking).

The test also covers emergency stopping — with ABS, apply firm continuous pressure and steer normally. Without ABS, use controlled braking to avoid lockup. Brake fade (brakes overheat and lose effectiveness going downhill) is a common question topic — the answer is always to use engine braking first and service brakes periodically, not continuously.

5. Vehicle Systems Knowledge

You don’t need to be a mechanic, but you need to understand enough about major systems to recognize problems. The test covers:

• Cooling systems — engine temperature warning signs, what to do if the temperature gauge rises
• Electrical systems — warning lights and what each means
• Fuel systems — no smoking near fuel tanks, fuel system leaks are a safety hazard
• Exhaust systems — leaks in the exhaust system are particularly dangerous because carbon monoxide can enter the cab

6. Hazardous Materials Basics

Even if you’re not pursuing the hazmat (H) endorsement, the General Knowledge test includes some basic hazmat content — specifically, the nine hazard classes and when placarding is required. If you want to earn the H endorsement, there’s a separate, more detailed hazmat knowledge test. Our hazmat placards and shipping papers guide covers the full endorsement content.

7. Transporting Passengers (Basic)

Basic rules about passenger transport show up in the General Knowledge test even if you don’t pursue the passenger (P) endorsement. Common topics include the prohibition on using a handheld phone while driving passengers, rules for loading and unloading at bus stops, and procedures at railroad crossings for passenger vehicles.

The Air Brakes and Combination Vehicles Tests

These are separate tests from the General Knowledge test, but many drivers take them at the same time they get their CLP. If you plan to drive a tractor-trailer (Class A with air brakes), you’ll need to pass both.

The Air Brakes test covers the S-cam air brake system, spring brakes, dual air systems, and the pre-trip brake inspection procedure. Key numbers to know: low pressure warning activates at or above 60 psi; spring brakes automatically apply between 20–45 psi; system cut-out pressure is 120–135 psi; cut-in pressure is around 100 psi.

Passing the Air Brakes test removes the L restriction from your CDL, which restricts you to vehicles without air brakes. Passing the Combination Vehicles test covers coupling and uncoupling, trailer swing (off-tracking), and rearward amplification in doubles and triples. Our dedicated CDL air brakes and combination vehicles test guide covers these in full detail.

Study Strategies That Actually Work

The CDL manual is the source of truth — everything on the test comes from it. But just reading it once rarely leads to a passing score. Here’s what works better:

Free practice tests are available from most state DMV websites and from several commercial CDL prep sites. Use your state’s official resources first — the question style and focus areas match your actual test most closely.

Frequently Asked Questions