Combination

What is a Combination Vehicle?

 

A combination vehicle is a vehicle with a tractor (truck) connected to one or more trailers. Combination vehicles are more difficult to drive due to their size and because the different parts of the vehicle can react differently to steering, braking, and acceleration.

 

Examples of Combination Vehicles:

 

    • Tractor-trailers (semi-trucks)

 

    • Double trailers (two connected trailers)

 

    • Triples (three connected trailers)

 

Coupling and Uncoupling

 

Coupling and uncoupling trailers safely is a crucial skill for driving combination vehicles.

 

  • Coupling refers to connecting the tractor to the trailer using a fifth-wheel coupling system.

 

Steps to Coupling:

 

1. Inspect the fifth wheel: Ensure that the locking jaws are open and properly lubricated.

 

2. Position the tractor: Back the tractor slowly under the trailer until the kingpin is engaged in the fifth wheel.

 

3. Secure the connection: After coupling, check the locking mechanism to ensure the trailer is properly attached.

 

Important: Always perform a tug test by gently pulling forward to check that the coupling is secure before driving away.

 

  • Uncoupling refers to safely disconnecting the tractor from the trailer.

 

Steps to Uncoupling:

 

1. Lower the landing gear: Ensure the trailer is stable on its landing gear before disconnecting.

 

2. Release the fifth wheel: Pull the release handle to unlock the fifth wheel.

 

3. Pull the tractor forward: Slowly drive the tractor away from the trailer.

 

Vehicle Inspection for Combination Vehicles

 

A thorough inspection of your combination vehicle is crucial for safety. The inspection must cover both the tractor and the trailer.

 

Key Inspection Points:

 

  • Air and Electrical Connections: Check that the air hoses and electrical lines between the tractor and trailer are securely connected and free of damage.

 

  • Brakes: Ensure both the tractor and trailer brakes are functioning properly.

 

  • Fifth Wheel Connection: Check that the coupling is secure and that the locking jaws have fully closed around the trailer’s kingpin.

 

  • Trailer Suspension: Check that the trailer suspension is in good condition and that the landing gear is fully raised.

 

Driving Combination Vehicles

 

Driving a combination vehicle requires extra caution due to the size and dynamics of the vehicle.

 

Turns:

 

  • Combination vehicles require wider turns, especially to the right.

 

  • The trailer will track inside the path of the tractor during turns, so you must begin turns wider than you would in a smaller vehicle.

 

Backing Up:

 

  • Backing up a combination vehicle is more challenging because the trailer can swing out in unexpected directions. Go slow and use your mirrors.

 

  • When backing up, turn the steering wheel in the opposite direction of where you want the trailer to go.

 

Stopping Distance:

 

  • Combination vehicles take longer to stop due to their weight. Always maintain a larger following distance to account for this.

 

  • Brake early and gently, especially when the trailer is empty, as it can cause the trailer to skid or jackknife.

 

Preventing Skids and Jackknifing

 

Skidding and jackknifing are major risks when driving combination vehicles, particularly in slippery conditions.

 

Skid Prevention:

 

  • Drive Slowly: Reducing speed helps prevent skids, especially on wet or icy roads.

 

  • Avoid Abrupt Braking: Never slam on the brakes, as this can lock up the trailer’s wheels, leading to a skid.

 

  • Even Braking: Use steady pressure on the brakes and avoid using the trailer brakes alone.

 

 

Jackknifing:

 

    • Jackknifing occurs when the trailer swings out of line with the tractor, forming a 90-degree angle. It usually happens during sudden braking or on slippery surfaces.

 

How to Prevent Jackknifing:

 

1. Brake Early: Slow down gradually and brake well before intersections or turns.

 

2. Do Not Oversteer: Avoid making sharp steering movements.

 

3. Use Engine Braking: Shift into a lower gear to help slow the vehicle down on downhill grades.

 

Rollover Risks

 

Combination vehicles, especially those with high centers of gravity, are at greater risk of rolling over.

 

Causes of Rollovers:

 

    • Taking turns too fast

 

    • Sudden steering movements

 

    • Shifting cargo

 

Preventing Rollovers:

 

1. Slow Down: Take turns slowly, especially on curves.

 

2. Load Cargo Correctly: Ensure that the load is balanced and secured.

 

3. Stay Focused: Always be aware of road conditions and adjust your driving accordingly.

 

Trailer Sway and Off-Tracking

 

Combination vehicles can experience trailer sway, where the trailer moves side to side. This can be caused by high winds, improper loading, or sudden steering movements.

 

Preventing Trailer Sway:

 

  • Slow Down: Reduce speed in windy conditions or when going downhill.

 

  • Load Properly: Ensure the trailer is loaded with weight evenly distributed.

 

  • Avoid Sudden Steering: Make slow and smooth steering adjustments.

 

Off-Tracking:

 

  • Off-tracking happens when the trailer follows a different path than the tractor during turns. The rear of the trailer swings wide and can collide with objects on the side of the road.

 

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