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Railroad crossings, trailer skids, wide turns and backing

Combination Vehicles4 minManual section 6.1.4–6.1.7

Four everyday situations where a trailer behaves differently from a car: low trailers on raised railroad crossings, a skidding trailer, the rear wheels cutting corners, and backing where the steering works in reverse.

Railroad-highway crossings (6.1.4)

Trailers with low clearance underneath can get stuck (hung up) on a raised crossing. Know these types:

  • Low-slung units: lowboy, car carrier, moving van, and possum-belly livestock trailer.
  • A single-axle tractor pulling a long trailer whose landing gear is set for a tandem-axle tractor (the trailer sits lower than it should).

If you get stuck on the tracks for any reason: get out of the vehicle and away from the tracks first. Then look on the signposts or signal housing at the crossing for emergency contact information. Call 911 or the other emergency number. Give the location using landmarks, especially the crossing's DOT number if it is posted.

Prevent and stop a trailer skid (6.1.5)

When the trailer wheels lock up, the trailer tends to swing around. This is a trailer jackknife. It is more likely when the trailer is empty or lightly loaded.

Two steps to stop a trailer skid:

  • Recognize the skid. The earliest and best way is to see it in your mirrors. Every time you brake hard, check the mirrors to make sure the trailer stays where it belongs. Once the trailer swings out of your lane, a jackknife is very hard to prevent.
  • Stop using the brake. Release the brakes so the wheels can grip again. Do not use the trailer hand brake to "straighten out the rig" — the trailer brakes caused the skid in the first place. When the trailer wheels get traction back, the trailer follows the tractor and straightens out.

Turn wide: off-tracking (6.1.6)

In a turn, the rear wheels follow a shorter, inside path than the front wheels. This is off-tracking, also called "cheating". It makes the path of the rig wider than the rig itself.

  • Longer vehicles off-track more.
  • The rear wheels of the tractor off-track some; the rear wheels of the trailer off-track more.
  • With more than one trailer, the rear wheels of the last trailer off-track the most.

Steer the front end wide enough that the rear does not run over the curb or pedestrians. But keep the rear of the vehicle close to the curb, so other drivers cannot pass you on the right.

If the turn cannot be made without using another lane, swing wide near the end of the turn, not at the start. Swinging out to the left before turning leaves a gap on your right that other drivers may try to pass through.

Backing with a trailer (6.1.7)

When you back a car, straight truck or bus, you turn the wheel's top toward where you want to go. When backing a trailer, you turn the wheel the opposite way. Once the trailer begins to turn, turn the wheel back the other way to follow it.

Whenever you can, line up so you can back straight. If the path must curve, back toward the driver's side, where you can see.

Safe backing rules:

  • Look at your path before you begin. Get out and walk around. Check side and overhead clearance in and near your path.
  • Use the mirrors on both sides often. Get out and check again if you are unsure.
  • Back slowly, so you can correct before you get far off course.
  • Correct drift immediately: when the trailer moves off the path, turn the top of the wheel toward the drift.
  • Pull forward (pull-ups) to reposition when you need to.

References and scope

The topic reference is listed below. Sources support verification; the lesson itself is here. The current content needs technical and language review before public launch.

Manual reference: 6.1.4–6.1.7

Official CDL handbook · Utah ↗StatesOur editorial approach

Put it into practice

Educational questions with explanations. The answer review also works without the interactive quiz.

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Review questions with answers

  1. Which trailer is most likely to get stuck (hung up) on a raised railroad crossing?
    1. A dry van with normal ground clearance
    2. A lowboy
    3. A flatbed with high clearance
    4. A tank trailer with tandem axles set correctly
    Show answer
    A lowboy

    Low-slung units like lowboys, car carriers, moving vans and possum-belly livestock trailers can hang up.

  2. A single-axle tractor pulls a long trailer whose landing gear is set for a tandem-axle tractor. What is the risk?
    1. The trailer brakes will not release
    2. The fifth wheel will not lock
    3. The tractor protection valve will close
    4. The trailer may get stuck on a raised railroad crossing
    Show answer
    The trailer may get stuck on a raised railroad crossing

    This setup leaves the trailer riding low, so it can hang up on raised crossings.

  3. Your trailer gets stuck on the railroad tracks. What should you do first?
    1. Get out of the vehicle and away from the tracks
    2. Try to rock the rig back and forth
    3. Stay in the cab and call your dispatcher
    4. Lower the landing gear
    Show answer
    Get out of the vehicle and away from the tracks

    First get out and away from the tracks, then find the emergency info and call.

  4. When you report a vehicle stuck on a railroad crossing, which number is most helpful to give?
    1. Your CDL number
    2. The trailer license plate
    3. The crossing's DOT number, if posted
    4. The truck's VIN
    Show answer
    The crossing's DOT number, if posted

    Give the location using landmarks, especially the DOT number of the crossing.

  5. A trailer jackknife (trailer skid) is most likely when the trailer is:
    1. Fully loaded
    2. Empty or lightly loaded
    3. Equipped with ABS
    4. Coupled with a sliding fifth wheel
    Show answer
    Empty or lightly loaded

    Trailer wheels lock up more easily when the trailer is empty or lightly loaded.

  6. What is the earliest and best way to recognize that your trailer has started to skid?
    1. Feeling it in the steering wheel
    2. Hearing the tires squeal
    3. Seeing it in your mirrors
    4. A warning light on the dash
    Show answer
    Seeing it in your mirrors

    The best early sign is seeing the trailer move in your mirrors. Check them whenever you brake hard.

  7. Your trailer starts to skid because its wheels locked. What should you do?
    1. Release the brakes so the trailer wheels can regain traction
    2. Apply the trailer hand brake to straighten the rig
    3. Brake harder with the foot brake
    4. Turn sharply toward the trailer
    Show answer
    Release the brakes so the trailer wheels can regain traction

    Stop using the brake. Once the trailer wheels grip again, the trailer will follow the tractor and straighten out.

  8. Your trailer is skidding and starting to jackknife. Why is the trailer hand brake the wrong tool to straighten it out?
    1. It releases the tractor brakes
    2. It closes the tractor protection valve
    3. It only works above 40 mph
    4. The trailer brakes caused the skid in the first place
    Show answer
    The trailer brakes caused the skid in the first place

    Locked trailer wheels caused the skid, so applying more trailer brake makes it worse.

  9. Once the trailer swings out of your lane in a skid:
    1. It is easy to correct with the hand valve
    2. It is very difficult to prevent a jackknife
    3. ABS will always straighten it
    4. You should accelerate hard
    Show answer
    It is very difficult to prevent a jackknife

    Once the trailer leaves your lane, a jackknife is very hard to prevent, so catch it early in the mirrors.

  10. What is off-tracking?
    1. The trailer sliding sideways on ice
    2. Drifting out of your lane on a straight road
    3. Rear wheels following a different, shorter path than the front wheels in a turn
    4. Trailer wheels locking up
    Show answer
    Rear wheels following a different, shorter path than the front wheels in a turn

    Off-tracking (cheating) is when the rear wheels follow a different path than the front wheels when turning.

  11. In a set of doubles, which wheels off-track the most?
    1. The rear wheels of the last trailer
    2. The tractor's front wheels
    3. The tractor's rear wheels
    4. The first trailer's front wheels
    Show answer
    The rear wheels of the last trailer

    The more trailers, the more off-tracking; the last trailer's rear wheels off-track the most.

  12. Why should you keep the rear of your vehicle close to the curb in a right turn?
    1. To reduce tire wear
    2. To use less fuel
    3. To keep the trailer from rolling over
    4. To stop other drivers from passing you on the right
    Show answer
    To stop other drivers from passing you on the right

    Keeping the rear close to the curb prevents other drivers from slipping by on the right.

  13. If you cannot make a right turn without entering another lane, what should you do?
    1. Swing wide to the left before starting the turn
    2. Turn wide as you complete the turn
    3. Back up and try again
    4. Drive over the curb
    Show answer
    Turn wide as you complete the turn

    Turning wide as you complete the turn is better than swinging left first, which invites passing on the right.

  14. Longer vehicles off-track:
    1. More
    2. Less
    3. The same as short vehicles
    4. Only when loaded
    Show answer
    More

    Longer vehicles off-track more.

  15. When backing a trailer, which way do you first turn the steering wheel?
    1. The same direction you want the trailer to go
    2. Straight; do not turn
    3. Opposite the direction you want the trailer to go
    4. Always to the right
    Show answer
    Opposite the direction you want the trailer to go

    With a trailer you turn the wheel opposite to the way you want to go; then follow the trailer.

  16. True or False: If you must back a trailer on a curve, you should set up to back toward the passenger side.
    1. True
    2. False
    Show answer
    False

    False. Try to back in a straight line; if you must curve, back toward the driver's side so you can see.

  17. While backing, the trailer starts to drift off the proper path. How do you correct it?
    1. Pull the trailer hand valve
    2. Stop and set the parking brake for 1 minute
    3. Turn the top of the wheel away from the drift
    4. Turn the top of the steering wheel toward the drift
    Show answer
    Turn the top of the steering wheel toward the drift

    Fix drift right away: turn the top of the steering wheel toward the side the trailer is drifting to.

  18. Which is a safe backing practice with a trailer?
    1. Get out and walk around to check your path and overhead clearance
    2. Back quickly to finish before traffic arrives
    3. Use only the driver's-side mirror
    4. Never pull forward once you start backing
    Show answer
    Get out and walk around to check your path and overhead clearance

    Look at your path first: get out and walk around, checking side and overhead clearance.

  19. Why should you back a trailer slowly?
    1. To keep the air pressure up
    2. To keep the trailer brakes cool
    3. So you can correct before getting too far off course
    4. Because the transmission has only one reverse gear
    Show answer
    So you can correct before getting too far off course

    Backing slowly lets you make corrections before you get far off course.