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Commercial driver’s license (CDL) knowledge tests · California DMV

Driving Combination Vehicles Safely

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Questions and answers

  1. What causes more than half of truck driver deaths in accidents?

    Truck rollovers

    More than half of truck driver deaths in accidents result from rollovers.

    Section 6 · 6.1.1 – Rollover Risks ↗

  2. What happens to the center of gravity when more cargo is piled up in a truck?

    It moves higher up from the road and the truck becomes easier to turn over

    Piled-up cargo raises the center of gravity and makes a rollover easier.

    Section 6 · 6.1.1 – Rollover Risks ↗

  3. How much more likely are fully loaded rigs to roll over in an accident than empty rigs?

    10 times more likely

    A fully loaded rig is 10 times more likely to roll over in an accident than an empty one.

    Section 6 · 6.1.1 – Rollover Risks ↗

  4. Which two things will help you prevent a rollover?

    Keep the cargo as close to the ground as possible and drive slowly around turns

    Low cargo and slow turns are the two keys to preventing rollover.

    Section 6 · 6.1.1 – Rollover Risks ↗

  5. Where is keeping cargo low even more important?

    In combination vehicles, more than in straight trucks

    Keeping cargo low matters even more in a combination vehicle than in a straight truck.

    Section 6 · 6.1.1 – Rollover Risks ↗

  6. The load sits to one side and makes the trailer lean. What is the effect?

    A rollover is more likely

    Keep the load centered and spread out as much as possible, because a leaning trailer rolls over more easily.

    Section 6 · 6.1.1 – Rollover Risks ↗

  7. When do rollovers happen?

    When you turn too fast

    Rollovers happen when you turn too fast, so drive slowly around corners, on ramps, and off ramps.

    Section 6 · 6.1.1 – Rollover Risks ↗

  8. What should you avoid, especially when fully loaded?

    Quick lane changes

    Quick lane changes can roll a fully loaded rig.

    Section 6 · 6.1.1 – Rollover Risks ↗

  9. What can the “crack-the-whip” effect do when you make a quick lane change?

    Turn the trailer over

    A quick lane change can whip the trailer over. In many accidents only the trailer has overturned.

    Section 6 · 6.1.2 – Steer Gently ↗

  10. What causes the crack-the-whip effect?

    Rearward amplification

    Rearward amplification is the cause of the crack-the-whip effect.

    Section 6 · 6.1.2 – Steer Gently ↗

  11. What does a rearward amplification of 2.0 mean?

    The rear trailer is twice as likely to turn over as the tractor

    A value of 2.0 means the rear trailer turns over twice as easily as the tractor.

    Section 6 · 6.1.2 – Steer Gently ↗

  12. What rearward amplification do triples have?

    3.5

    Triples have a rearward amplification of 3.5.

    Section 6 · 6.1.2 – Steer Gently ↗

  13. What does the rearward amplification of triples mean in practice?

    You can roll the last trailer 3.5 times as easily as a 5-axle tractor

    The last trailer of triples rolls 3.5 times as easily as a 5-axle tractor.

    Section 6 · 6.1.2 – Steer Gently ↗

  14. How should you steer when you are pulling trailers?

    Gently and smoothly

    A sudden steering movement could tip the trailer over.

    Section 6 · 6.1.2 – Steer Gently ↗

  15. How far should you follow behind other vehicles when pulling trailers?

    At least 1 second for each 10 feet of vehicle length, plus another second if going over 40 mph

    Allow 1 second per 10 feet of your vehicle length and add 1 second above 40 mph.

    Section 6 · 6.1.2 – Steer Gently ↗

  16. You are driving a 60-foot combination at 50 mph. What is the least following distance you should keep?

    7 seconds

    Six seconds for 60 feet of length, plus one more second because the speed is over 40 mph.

    Section 6 · 6.1.2 – Steer Gently ↗

  17. You are driving a 50-foot combination at 30 mph. What is the least following distance you should keep?

    5 seconds

    One second for each 10 feet gives 5 seconds, and no extra second is added at 40 mph or less.

    Section 6 · 6.1.2 – Steer Gently ↗

  18. How fast should you drive at night when pulling trailers?

    Slowly enough to see obstacles with your headlights before it is too late to change lanes or stop gently

    At night your speed must let you see obstacles in time to react gently.

    Section 6 · 6.1.2 – Steer Gently ↗

  19. When should you slow down for a turn?

    Before going into the turn

    Slow to a safe speed before you enter the turn.

    Section 6 · 6.1.2 – Steer Gently ↗

  20. Why should you look far enough down the road when pulling trailers?

    To avoid being surprised and having to make a sudden lane change

    Looking far ahead prevents surprises that force sudden lane changes.

    Section 6 · 6.1.2 – Steer Gently ↗

  21. When do large combination vehicles take longer to stop?

    When they are empty

    Large combination vehicles take longer to stop when empty than when fully loaded.

    Section 6 · 6.1.3 – Brake Early ↗

  22. Why is it very easy to lock up the wheels of a lightly loaded combination?

    The very stiff suspension springs and strong brakes give poor traction

    With a light load, stiff springs and strong brakes give poor traction.

    Section 6 · 6.1.3 – Brake Early ↗

  23. What is a “bobtail” tractor?

    A tractor without a semitrailer

    A bobtail is a tractor running without a semitrailer.

    Section 6 · 6.1.3 – Brake Early ↗

  24. How does the stopping of a bobtail compare with a tractor-semitrailer loaded to maximum gross weight?

    The bobtail takes longer to stop

    Bobtails can be very hard to stop smoothly and take longer to stop than a fully loaded tractor-semitrailer.

    Section 6 · 6.1.3 – Brake Early ↗

  25. What should you do in any combination rig so that you can brake early?

    Allow lots of following distance and look far ahead

    Plenty of following distance and a far look ahead keep you from making a panic stop.

    Section 6 · 6.1.3 – Brake Early ↗

  26. Which kind of trailer can get stuck on a raised railroad crossing?

    A low slung unit such as a lowboy, car carrier, moving van, or possum-belly livestock trailer

    Trailers with low underneath clearance can hang up on raised crossings.

    Section 6 · 6.1.4 – Railroad-Highway Crossings ↗

  27. Which tractor and trailer setup can get stuck on a raised railroad crossing?

    A single-axle tractor pulling a long trailer with its landing gear set for a tandem-axle tractor

    Landing gear set to suit a tandem-axle tractor hangs low behind a single-axle tractor.

    Section 6 · 6.1.4 – Railroad-Highway Crossings ↗

  28. Your rig gets stuck on railroad tracks. What do you do first?

    Get out of the vehicle and away from the tracks

    Get out and away from the tracks, then call 9-1-1 or another emergency number.

    Section 6 · 6.1.4 – Railroad-Highway Crossings ↗

  29. Where do you look for emergency notification information when stuck at a crossing?

    On signposts or the signal housing at the crossing

    Check the signposts or signal housing at the crossing.

    Section 6 · 6.1.4 – Railroad-Highway Crossings ↗

  30. When you report being stuck on the tracks, what should you give, if it is posted?

    The DOT number of the crossing, along with identifiable landmarks

    Give the location using all identifiable landmarks, especially the DOT number.

    Section 6 · 6.1.4 – Railroad-Highway Crossings ↗

  31. What happens when the wheels of a trailer lock up?

    The trailer will tend to swing around

    A trailer with locked wheels tends to swing around. This is often called a trailer jackknife.

    Section 6 · 6.1.5 – Prevent Trailer Skids ↗

  32. When is a trailer jackknife more likely to happen?

    When the trailer is empty or lightly loaded

    An empty or lightly loaded trailer locks its wheels and swings out more easily.

    Section 6 · 6.1.5 – Prevent Trailer Skids ↗

  33. What is the earliest and best way to recognize that the trailer has started to skid?

    Seeing it in your mirrors

    Any time you brake hard, check the mirrors to see that the trailer is staying where it should be.

    Section 6 · 6.1.5 – Prevent Trailer Skids ↗

  34. Why is early recognition of a trailer skid so important?

    Once the trailer swings out of your lane, it is very difficult to prevent a jackknife

    After the trailer leaves your lane a jackknife is very hard to prevent.

    Section 6 · 6.1.5 – Prevent Trailer Skids ↗

  35. Your trailer starts to skid. What do you do with the brakes?

    Release them to get traction back

    Stop using the brake. Once the trailer wheels grip again, the trailer follows the tractor and straightens out.

    Section 6 · 6.1.5 – Prevent Trailer Skids ↗

  36. Why should you not use the trailer hand brake to straighten out a skidding trailer?

    The brakes on the trailer wheels caused the skid in the first place

    More trailer braking keeps the trailer wheels locked and sliding.

    Section 6 · 6.1.5 – Prevent Trailer Skids ↗

  37. What is off-tracking, or “cheating”?

    The rear wheels follow a different path than the front wheels in a turn

    In a corner the rear wheels do not follow the path of the front wheels.

    Section 6 · 6.1.6 – Turn Wide ↗

  38. Which vehicles off-track more?

    Longer vehicles

    The longer the vehicle, the more it off-tracks.

    Section 6 · 6.1.6 – Turn Wide ↗

  39. In a rig with more than one trailer, which wheels off-track the most?

    The rear wheels of the last trailer

    Each unit off-tracks more than the one ahead, and the last trailer off-tracks the most.

    Section 6 · 6.1.6 – Turn Wide ↗

  40. Why should you keep the rear of your vehicle close to the curb in a right turn?

    It stops other drivers from passing you on the right

    Steer the front wide enough to clear the curb, but keep the rear close so nobody passes on the right.

    Section 6 · 6.1.6 – Turn Wide ↗

  41. You cannot complete a turn without entering another traffic lane. How should you turn?

    Turn wide as you complete the turn

    Going wide at the end of the turn is better than swinging left first, which invites drivers to pass on the right.

    Section 6 · 6.1.6 – Turn Wide ↗

  42. When you start backing a trailer, which way do you turn the steering wheel?

    In the direction opposite to the way you want the trailer to go

    A car, straight truck, or bus is steered toward where you want to go. A trailer is the opposite.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  43. Once the trailer starts to turn while backing, what do you do?

    Turn the wheel the other way to follow the trailer

    After the trailer starts turning, steer the other way to follow it.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  44. How should you try to position your vehicle whenever you back with a trailer?

    So you can back in a straight line

    Straight-line backing is the first choice.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  45. You must back on a curved path. Toward which side should you back?

    Toward the driver’s side, so you can see

    Backing toward the driver’s side lets you see where you are going.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  46. What should you do before you begin backing with a trailer?

    Get out and walk around the vehicle to look at your line of travel and clearances

    Look at your path and check clearance to the sides and overhead, in and near the path of the vehicle.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  47. How often should you check the outside mirrors while backing a trailer?

    Frequently, on both sides

    Check the mirrors on both sides frequently, and get out to re-inspect the path if you are unsure.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  48. Why should you back slowly with a trailer?

    So you can make corrections before you get too far off course

    Slow backing leaves time to correct.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  49. While backing, you see the trailer getting off the proper path. How do you correct it?

    Turn the top of the steering wheel in the direction of the drift, right away

    Correct drift immediately by turning the top of the wheel toward the drift.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

  50. What should you do when backing a trailer if the vehicle needs repositioning?

    Pull forward and reposition as needed

    Make pull-ups to reposition the vehicle whenever needed.

    Section 6 · 6.1.7 – Backing With a Trailer ↗

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