CDL Combination Vehicles Study Guide

Introduction

The CDL Combination Vehicles test is designed to assess your knowledge of operating combination vehicles, which include tractor-trailers, doubles, triples, and other configurations. Understanding the unique challenges and safety requirements of driving combination vehicles is essential for passing this test and safely operating these vehicles on the road. This guide covers the key topics you’ll need to study.

1. Understanding Combination Vehicles

Definition: A combination vehicle is made up of a tractor (also called a power unit) and one or more trailers. These vehicles are typically longer and heavier than single-unit vehicles.
Types of Combination Vehicles:
- Tractor-Semitrailer: The most common type, consisting of a tractor and a single trailer.
- Doubles and Triples: Combinations that include more than one trailer. These require special handling and additional endorsements.

2. Key Components of Combination Vehicles

Fifth Wheel: The coupling device used to connect the tractor to the trailer. Understanding its parts and functions is crucial for safe operation.
Kingpin: The pin on the trailer that fits into the fifth wheel and locks the trailer in place.
Glad Hands: Couplings used to connect the air lines between the tractor and the trailer.

3. Coupling and Uncoupling

Coupling Procedure:
- Inspect the Fifth Wheel: Ensure it’s properly greased and securely mounted.
- Position the Tractor: Align the tractor with the trailer, ensuring the fifth wheel is directly below the kingpin.
- Back Slowly: Back the tractor until the fifth wheel touches the trailer, then stop and apply the parking brake.
- Secure the Kingpin: Lift the trailer landing gear slightly to check that the fifth wheel is locked onto the kingpin.
- Connect Air Lines and Electrical Lines: Ensure that the service and emergency lines are properly connected and that the electrical lines are secure.
- Check the Connection: Perform a tug test to ensure the trailer is securely connected.
Uncoupling Procedure:
- Park on Level Ground: This prevents the trailer from rolling.
- Lower the Landing Gear: Raise the trailer slightly off the fifth wheel.
- Disconnect Air and Electrical Lines: Store lines in their appropriate holders.
- Unlock the Fifth Wheel: Pull the release handle to unlock the fifth wheel.
- Slowly Pull Forward: Move the tractor forward until the trailer is clear of the fifth wheel.

4. Air Brakes on Combination Vehicles

Service Lines and Emergency Lines:
- Service Line (Blue): Controls the application of the trailer brakes.
- Emergency Line (Red): Supplies air to the trailer’s air tanks and controls emergency brakes.
Breakaway and Emergency Systems:
- Emergency Brakes: Automatically apply if the trailer becomes disconnected or if there is a loss of air pressure.
- Breakaway Cable: Mechanically applies the trailer brakes in case the trailer detaches from the tractor.
Anti-Lock Braking System (ABS): Most combination vehicles are equipped with ABS, which prevents the wheels from locking during hard braking. Learn to recognize the ABS malfunction light and understand its function.

5. Preventing Trailer Skids

Causes of Skids: Trailer skids are often caused by over-braking, over-steering, or over-acceleration.
Preventing Skids:
- Proper Braking: Apply brakes gradually and evenly.
- Maintain Traction: Avoid sudden movements that could cause a loss of traction.
- Load Distribution: Ensure the load is evenly distributed and properly secured.
Correcting a Skid:
- Identify a Skid: The most common type of skid in combination vehicles is the trailer jackknife.
- Responding to a Skid: Release the brakes to regain traction and gently steer in the direction you want to go.

6. Managing Turns and Backing Up

Turning with Combination Vehicles:
- Wide Turns: Remember that combination vehicles need more space to turn, especially to the right. Watch your trailer’s path and be mindful of the off-tracking effect (where the trailer wheels follow a different path than the tractor wheels).
- Left Turns: Left turns require a wide berth as well, but generally provide more visibility. Ensure that oncoming traffic is clear before completing the turn.
Backing Up a Combination Vehicle:
- Straight-Line Backing: Align the tractor and trailer in a straight line and back up slowly, using mirrors to keep the trailer straight.
- Alley Docking: Turn the wheel in the opposite direction of where you want the trailer to go. Use small adjustments and frequently check both mirrors.
- Sight-Side Backing: Backing up towards the driver’s side is easier and safer as it provides better visibility.

7. Driving Combination Vehicles Safely

Speed Management:
- On Curves: Reduce speed before entering a curve to prevent rollover.
- On Grades: Downshift before starting down a grade and use engine braking to help control speed.
Space Management:
- Following Distance: Increase following distance to account for the longer stopping distance required by combination vehicles.
- Clearances: Be aware of overhead and side clearances, especially when pulling doubles or triples.
Accident Prevention:
- Stopping Distance: Remember that combination vehicles require longer distances to stop, especially when loaded.
- Weather Conditions: In wet or icy conditions, increase following distance and reduce speed to prevent skids and jackknifing.

8. Understanding Rollovers

Causes of Rollovers: Rollovers can occur due to excessive speed, sharp turns, or uneven load distribution.
Preventing Rollovers: Drive at safe speeds, avoid sudden maneuvers, and ensure the load is balanced and properly secured.

9. Special Considerations for Doubles and Triples

Turning and Lane Changes: Doubles and triples require more space for turns and lane changes. Always signal well in advance and check mirrors carefully.
Stability: These combinations are less stable than single trailers, so avoid sudden movements and reduce speed on curves and during lane changes.

10. Pre-Trip Inspection for Combination Vehicles

Coupling System: Inspect the fifth wheel, kingpin, and locking jaws for wear and proper engagement.
Air Lines: Check for leaks, proper connections, and secure mounting.
Brakes: Ensure proper brake adjustment and inspect for any signs of wear or damage.
Lights and Reflectors: Verify that all lights and reflectors are working and clean.
Trailer: Inspect the trailer’s frame, suspension, and tires for any damage or issues.

Conclusion

The CDL Combination Vehicles test requires a solid understanding of the specific challenges and safety practices involved in operating these types of vehicles. By studying the topics outlined in this guide, you will be well-prepared to pass the test and handle combination vehicles with confidence. For additional study materials and practice tests, visit FreightRelocators.com.

This study guide provides a comprehensive overview of the key areas you need to focus on to prepare for the CDL Combination Vehicles test. Understanding these concepts will help ensure your success on the test and your safety on the road.

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