CDL General Knowledge Test: What's on It and How to Study

The CDL General Knowledge test is the first written exam every CDL applicant must pass. It's the broadest test — covering everything from pre-trip inspection to mountain driving to hours of service. This guide breaks down every topic, gives you the specific facts most people miss, and shows you the fastest study path. Start with a free CDL General Knowledge practice test to see where you stand.

Test Format: What to Expect at the DMV

• Number of questions: Most states use 50 questions (some use 30–40)
• Passing score: 80% — you can miss up to 10 on a 50-question test
• Format: Multiple choice, computer-based, taken at your state DMV
• Time limit: Usually 60 minutes, but varies by state
• Retake policy: Most states allow next-day retakes; some impose a waiting period or retest fee ($10–$25)
• Language: English in most states; some offer Spanish

The 12 Topic Areas (and What's Tested in Each)

1. Vehicle Inspection

Pre-trip, en-route, and post-trip inspection procedures. You must know the 7-step inspection method, what to check on each vehicle type, and how to report defects. Key rule: if a defect is safety-related, the vehicle must not be operated until it's repaired. Read our full pre-trip inspection guide.

2. Basic Vehicle Control

Starting, stopping, steering, and backing. Key concepts: accelerate smoothly, brake early and gradually, do not oversteer. Backing procedures include straight-line backing, alley dock, and parallel parking — these are tested in the skills test, but knowledge questions cover the principles.

3. Shifting Gears

Proper shifting technique for manual transmissions. Key concepts: double-clutching (depress clutch twice — once to pull out of gear, once to engage the next gear), RPM range (shift up at 1,500–2,000 RPM for diesel engines), and skipping gears on downgrades. Know when to use lower gears: before starting down a hill, not after you've already gained momentum.

4. Seeing and Communicating

Visual search patterns, mirror use, blind spots, and communication with other drivers. Key numbers: your mirrors should show 200 feet behind the vehicle on each side. Use turn signals 100 feet before turning in town (5 mph zones), 500 feet on the highway. Hazard lights when stopped on the road: place warning devices within 10 minutes — triangles at 100 feet (front), 100 feet (rear), and 200 feet (rear, on divided highway).

5. Speed and Space Management

Following distance, stopping distance, and space management. Key numbers: 4 seconds following distance above 40 mph; 6–10 seconds in adverse weather. Stopping distance at 55 mph on dry pavement: approximately 300 feet for a loaded combination vehicle. Speed reduction on curves: reduce by 5–10 mph before entering, not during the curve.

6. Night Driving

Reduced visibility, headlight use, and fatigue management. Key rules: headlights must be on from sunset to sunrise and whenever visibility is less than 500 feet. Use high beams when there are no oncoming vehicles within 500 feet. Reduce speed by 1/3 on wet roads and 1/2 or more on packed snow.

7. Driving in Fog

Never use high beams in fog — they reflect off the fog and blind you. Use low beams. If visibility drops below 500 feet, reduce speed significantly. If you must stop, pull completely off the road and use hazard lights. Fog is most common in early morning and near bodies of water.

8. Winter Driving

Black ice (a thin, nearly invisible layer of ice) forms at 32°F and is most common on bridges and overpasses. Signs of black ice: ice on the mirror or antenna, or the road looks wet but spray from other vehicles stops. Carry chains in mountain states. Know how to install tire chains before you need to do it on a mountain pass at midnight.

9. Mountain Driving

Start in a low gear before beginning the descent — never shift down after you've gained speed. Use engine brake (Jake brake) to control speed. If your speed increases beyond a safe level, use the brakes hard for a few seconds, then release — this prevents brake fade from continuous light braking. Never pump air brakes — press firmly and hold.

10. Staying Alert and Fighting Fatigue

Signs of fatigue: heavy eyelids, frequent yawning, difficulty focusing, drifting from your lane, missing exits. The only real fix: stop and sleep. Opening a window or turning up the radio does NOT fix fatigue. Short naps of 15–45 minutes can temporarily restore alertness. Know the hours-of-service rules: maximum 11 hours driving after 10 consecutive hours off duty; 14-hour window; 60 hours in 7 days or 70 hours in 8 days.

11. Crash Procedures

If you're in an accident: 1) Protect the scene (set out warning devices), 2) Notify authorities (call 911), 3) Care for injured (do not move injured persons unless there's immediate danger like fire), 4) Document everything (photos, witness info, time, location). Never drive away from an accident scene — it's a felony.

12. Accident Prevention

Defensive driving principles: plan ahead for road conditions, maintain space around the vehicle, anticipate other drivers' mistakes. The most common causes of commercial vehicle crashes: following too closely, speeding, and distraction. Know the 2-second rule for passenger cars does NOT apply to commercial vehicles — use 4 seconds minimum.

ELDT Theory vs. the General Knowledge Test

These are two separate requirements. ELDT theory is a federal training course you complete with a registered provider. The General Knowledge test is a state DMV exam. They cover overlapping material — which is why our practice tests help with both. We recommend completing ELDT theory first because it systematically covers every topic that appears on the DMV test. You'll walk into the DMV already knowing the material.

The 5-Day Study Plan

Frequently Asked Questions