CDL General Knowledge Practice Test 2026

About the CDL General Knowledge exam

Also searched as: CDL practice test, CDL test. It's the same exam — CDL General Knowledge is the official name.

The Commercial Driver's License - General Knowledge (CDL General Knowledge) is a driving & permit examination administered in USA. It is designed to assess candidates' knowledge and proficiency across 7 key subject areas including General Knowledge, Air Brakes, Combination Vehicles, Hazmat Endorsement. This exam is widely recognized as an essential benchmark for obtaining a driver's license.

Use short CDL General Knowledge practice sets to identify topics to revisit. Choose a subject and difficulty, answer questions, then review the explanations. New accounts get 30 question credits; further new questions use paid credits. Retaking previously seen questions is free.

Whether you're a first-time candidate or retaking the CDL General Knowledge to improve your score, InfinityMock helps you identify your strengths and weaknesses through detailed performance analytics. Our platform covers General Knowledge, Air Brakes, Combination Vehicles, Hazmat Endorsement, Tanker Endorsement, Passenger Endorsement, Pre-Trip Inspection, with questions available at Easy, Medium, and Hard difficulty levels. Track your progress, review detailed explanations, and build the confidence you need to pass on exam day.

CDL General Knowledge — quick answers

CDL General Knowledge at a glance

8 free CDL General Knowledge practice questions (2026)

Answer these first — no signup, no card. Every answer is explained. For more practice, sign up for 30 free question credits and choose a subject above.

1. What is "liquid surge" and how does it affect the handling of a tanker?

   • The chemical reaction of liquids changing temperature during transit.
   • The rapid movement of liquid inside a partially filled tank when braking or accelerating.
   • The pressure buildup in the air brake lines when the trailer is loaded.
   • The expansion of liquid due to ambient heat outside the tank.
   Show answer & explanation

   Answer: B. The rapid movement of liquid inside a partially filled tank when braking or accelerating.

   Liquid surge is the movement of the liquid cargo inside a partially filled tank. When you brake, the liquid surges forward, pushing the truck. When you accelerate, it moves backward, pulling the truck.

   Topic: Tanker Endorsement · easy

2. Why must you leave "outage" (expansion space) when loading a liquid tanker?

   • To allow room for the liquid to expand as it warms up.
   • To prevent the liquid from surging during sudden stops.
   • To comply with weight limits on the steering axle.
   • To allow air to mix with the cargo for stability.
   Show answer & explanation

   Answer: A. To allow room for the liquid to expand as it warms up.

   Liquids expand when they warm up. Outage is the empty space left at the top of the tank to allow for this thermal expansion without causing structural damage or leaks.

   Topic: Tanker Endorsement · easy

3. Which of the following statements is TRUE regarding a "smoothbore" tanker?

   • It has bulkheads with small holes to slow down liquid movement.
   • It has no baffles to slow down the forward-and-back surge of liquid.
   • It is much easier to control during quick stops than a baffled tank.
   • It is only used for transporting highly volatile materials like gasoline.
   Show answer & explanation

   Answer: B. It has no baffles to slow down the forward-and-back surge of liquid.

   Smoothbore tanks have no internal baffles to slow down the forward and backward movement (surge) of liquid, making control during braking particularly hazardous.

   Topic: Tanker Endorsement · medium

4. How do liquid baffles inside a tanker affect side-to-side surge?

   • Baffles eliminate side-to-side surge completely.
   • Baffles have little to no effect on side-to-side surge.
   • Baffles increase side-to-side surge by channeling the liquid.
   • Baffles reduce side-to-side surge but increase forward surge.
   Show answer & explanation

   Answer: B. Baffles have little to no effect on side-to-side surge.

   Baffles are transverse barriers (running left to right) with holes that slow down forward and backward liquid surge. They do not run longitudinally, so they have little to no effect on side-to-side surge.

   Topic: Tanker Endorsement · hard

5. Why are partially filled tankers often more dangerous to drive than full tankers?

   • The total weight of a partially filled tanker is higher.
   • The air pressure inside a partially filled tank is highly unstable.
   • The movement of the liquid (surge) can destabilize the vehicle.
   • The brakes must work harder on a lighter load.
   Show answer & explanation

   Answer: C. The movement of the liquid (surge) can destabilize the vehicle.

   In a partially filled tank, there is room for the liquid to slosh back and forth. This movement (surge) shifts the vehicle's center of gravity rapidly, making it much harder to control than a completely full tank.

   Topic: Tanker Endorsement · medium

6. According to federal regulations, you must have a tanker endorsement (N) to drive a vehicle designed to transport liquid or gaseous materials in individual tanks of more than 119 gallons with an aggregate capacity of:

   • 500 gallons or more.
   • 800 gallons or more.
   • 1,000 gallons or more.
   • 5,000 gallons or more.
   Show answer & explanation

   Answer: C. 1,000 gallons or more.

   A tanker endorsement is required if the vehicle is designed to transport liquids or gases in individual tanks of more than 119 gallons and has an aggregate rated capacity of 1,000 gallons or more.

   Topic: Tanker Endorsement · medium

7. How does a tanker's high center of gravity affect its handling on curves and ramps?

   • It increases traction, allowing higher speeds on curves.
   • It makes the truck less likely to roll over than a standard dry van.
   • It requires you to drive much slower than the posted advisory speed limit for cars.
   • It reduces the effect of crosswinds on highway bridges.
   Show answer & explanation

   Answer: C. It requires you to drive much slower than the posted advisory speed limit for cars.

   Because tankers have a high center of gravity and liquid can shift side-to-side, they are highly prone to rolling over. Drivers must negotiate highway curves and off-ramps well below the posted advisory speed limits.

   Topic: Tanker Endorsement · easy

8. When braking to a stop in a tanker, what is the best way to manage the forward liquid surge?

   • Apply the brakes hard at the very end of the stop.
   • Keep steady, heavy pressure on the brakes until you come to a complete stop.
   • Release the brakes just before coming to a complete stop, then reapply.
   • Pump the brakes rapidly to break up the liquid wave.
   Show answer & explanation

   Answer: C. Release the brakes just before coming to a complete stop, then reapply.

   To prevent the forward surge from pushing your vehicle into an intersection or the vehicle ahead, you should release the brakes just before coming to a complete stop to let the surge settle, then reapply them.

   Topic: Tanker Endorsement · hard

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CDL General Knowledge Exam Subjects

Available practice subjects: General Knowledge, Air Brakes, Combination Vehicles, Hazmat Endorsement, Tanker Endorsement, Passenger Endorsement, Pre-Trip Inspection. Select a subject for focused preparation. Coverage is not a guarantee of the complete official syllabus.

📖 CDL General Knowledge Study Guide

Read our comprehensive How to Pass the CDL General Knowledge in 2026 — Complete Study Guide for expert preparation tips, study plans, and strategies.

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