Illinois CDL Combination Practice Test (IL) 2

4.8 out of 5 (189 votes)
80% Passing score
20 Questions
4 Mistakes allowed
Mastering the roadways of Illinois as a commercial driver requires in-depth knowledge and practical skills. Our Illinois CDL combination practice test is designed to provide you with the thorough preparation needed to succeed. This practice permit test includes 20 multiple-choice questions focusing on critical areas such as inspection procedures, safe driving practices, air brake systems, and more. With a passing requirement of at least 16 correct answers, you'll gain the confidence to ace the official test. Driving in Illinois presents unique challenges due to its diverse terrain and weather conditions. From the bustling streets of Chicago to the rural highways of Southern Illinois, each region has its own set of driving demands. For instance, navigating the icy roads during winter in the northern parts of the state or managing heavy traffic in urban areas requires specific skills that our Illinois CDL combination practice test will help you develop. Our combination vehicle test also emphasizes real-life scenarios, which are crucial for understanding the complexities of driving a combination vehicle. These scenarios prepare you for real-world situations, enhancing not just your test-taking abilities but also your overall driving competence. You'll learn about the risks of jackknifing, where the trailer swings out of alignment with the tractor. This dangerous situation can be avoided through smooth braking and careful handling, techniques that are covered in our practice questions. Each question on our Illinois DMV practice test is crafted and reviewed by professional driving instructors with decades of experience. Their expertise ensures that the questions are accurate, relevant, and challenging, providing you with a robust preparation tool. By practicing with questions that mirror those on the actual permit test, you'll be better equipped to handle the test day pressure and the diverse driving conditions across Illinois. Whether you're familiar with the scenic byways of the Shawnee National Forest or the busy interstates near St. Louis, this Illinois CDL combination practice test is tailored to meet the specific rules, regulations, and road signs of Illinois. Start your preparation today and move one step closer to achieving your commercial driving goals.
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Sample Illinois Combination Test Questions

Question 1

A combination vehicle with fewer axles is always more stable than one with more axles. True or false?

  1. A True
  2. B False

Correct answer: B – False

Fewer axles do not automatically make a combination vehicle more stable. The manual's examples show that some units with fewer axles have greater rearward amplification, increasing rollover risk during quick steering maneuvers. Drivers must understand the characteristics of their particular combination and steer gently and smoothly.

Source: Illinois CDL Study Guide — § 6.1.2, “Steer Gently,” including Figure 6.1

Question 2

What is the first listed step when coupling a tractor to a semitrailer?

  1. A Connect the air lines
  2. B Inspect the fifth wheel
  3. C Back completely under the trailer
  4. D Raise the landing gear

Correct answer: B – Inspect the fifth wheel

The first listed coupling step is to inspect the fifth wheel. Check for damage, secure mounting, required lubrication, open jaws, and the proper coupling position. A sliding fifth wheel must be locked, and the trailer kingpin must not be bent or broken before coupling continues.

Source: Illinois CDL Study Guide — § 6.4.1, “Coupling Tractor-Semitrailers—Step 1: Inspect Fifth-Wheel”

Question 3

Which practices help reduce rollover risk in a combination vehicle?

  1. A Keep the cargo close to the ground
  2. B Slow down before and through turns
  3. C Steer gently and smoothly
  4. D All of the above

Correct answer: D – All of the above

All three practices reduce rollover risk. Keeping cargo low limits the height of the center of gravity, while reducing speed before turns lowers the forces that can overturn the vehicle. Gentle, smooth steering also helps prevent the crack-the-whip effect from tipping a trailer during a sudden maneuver.

Source: Illinois CDL Study Guide — § 6.1.1, “Rollover Risks”; § 6.1.2, “Steer Gently”

Question 4

Rearward amplification produces the crack-the-whip effect in combination vehicles. True or false?

  1. A True
  2. B False

Correct answer: A – True

Rearward amplification causes the crack-the-whip effect. During an abrupt lane change or other quick steering maneuver, the rear portion of the combination can experience a greater rollover tendency than the tractor. Drivers should avoid sudden steering, leave adequate following distance, and reduce speed before entering turns.

Source: Illinois CDL Study Guide — § 6.1.2, “Steer Gently”

Question 5

What are the two functions of a trailer's emergency air line?

  1. A Operating the brake lights and electrical system
  2. B Cooling the brakes and inflating the tires
  3. C Supplying the trailer air tanks and controlling the emergency brakes
  4. D Operating the landing gear and fifth-wheel release

Correct answer: C – Supplying the trailer air tanks and controlling the emergency brakes

The emergency line, also called the supply line, delivers air to the trailer's storage tanks. It also controls the trailer emergency brakes. If pressure is lost because of a broken line, leak, or trailer separation, the emergency brakes apply and the tractor protection valve closes.

Source: Illinois CDL Study Guide — § 6.2.4, “Emergency Air Line”

Question 6

With the engine off and the brakes released, a combination vehicle's air loss should stay below which rate?

  1. A 1 psi per minute
  2. B 2 psi per minute
  3. C 3 psi per minute
  4. D 4 psi per minute

Correct answer: C – 3 psi per minute

Illinois lists a released-brake air-loss threshold of less than 3 psi in one minute for combination vehicles. The corresponding threshold for a single vehicle is less than 2 psi per minute. Do not confuse this with the fully applied-brake test, which allows no more than a 4 psi drop per minute for a combination vehicle.

Source: Illinois CDL Study Guide — § 5.3.3, “Test Air Leakage Rate”

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