{
  "slug": "combination-vehicles",
  "jurisdiction": "US",
  "name": "CDL Combination Vehicles",
  "kind": "combination-vehicles",
  "title": "CDL Combination Vehicles Practice",
  "language": "en",
  "edition": "March 2025",
  "questionCount": 40,
  "writtenTest": {
    "questionsAsked": 20,
    "correctToPass": 16,
    "confirmed": {
      "questionsAsked": false,
      "correctToPass": false,
      "passShare": true
    },
    "ruleSource": {
      "title": "49 CFR 383.135(b)(1) (80 percent to pass a CDL knowledge test)",
      "url": "https://www.ecfr.gov/current/title-49/subtitle-B/chapter-III/subchapter-B/part-383/subpart-F/section-383.135"
    },
    "note": "Federal rules require at least an 80 percent score on a CDL knowledge test. Twenty combination vehicles questions is the common state test size and the practice target here; the real test size and pass mark vary by state."
  },
  "disclaimer": "This is a study aid written by examprepare.help from the AAMVA model Commercial Driver's License Manual (Version March 2025), the model commercial driver's license manual that most states adopt. It is not the real CDL knowledge test, it is not affiliated with FMCSA, AAMVA or any state agency, and your state's test may differ. Check your state driver licensing agency before you take the real test.",
  "source": {
    "publisher": "American Association of Motor Vehicle Administrators (AAMVA), distributed by the Oklahoma Department of Public Safety; supported by the Federal Motor Carrier Safety Administration",
    "title": "Commercial Driver's License Manual, Modernized Testing System",
    "formNumber": null,
    "edition": "March 2025",
    "url": "https://aem-prod.oklahoma.gov/content/dam/service-oklahoma/Documents/CDLDriverManual.pdf",
    "pageUrl": "https://www.fmcsa.dot.gov/registration/commercial-drivers-license/cdl-manual",
    "retrieved": "2026-10-05",
    "textSha256": "1faa1b36ebbfaacdccfc7876fc5e75d02b5ea9d3b852dd22708d70b059c92672",
    "via": null
  },
  "facts": [
    {
      "key": "rollover-risk",
      "label": "Rollover risk of a fully loaded rig",
      "value": "Ten times more likely to roll over in a crash than an empty rig",
      "section": "6.1.1 – Rollover Risks",
      "page": 82
    },
    {
      "key": "amplification",
      "label": "Rearward amplification of triples",
      "value": "3.5 times as easy to roll the last trailer as a five-axle tractor",
      "section": "6.1.2 – Steer Gently",
      "page": 82
    },
    {
      "key": "tractor-protection",
      "label": "Pressure at which the tractor protection valve closes",
      "value": "20 to 45 psi",
      "section": "6.2.2 – Tractor Protection Valve",
      "page": 86
    },
    {
      "key": "air-line-colors",
      "label": "Air-line color code",
      "value": "Blue for service, red for emergency",
      "section": "6.2.4 – Trailer Air-lines",
      "page": 86
    },
    {
      "key": "shutoff-valves",
      "label": "Shut-off valve positions",
      "value": "Open except at the back of the last trailer, which is closed",
      "section": "6.2.7 – Shut-off Valves",
      "page": 87
    },
    {
      "key": "abs-trailer-date",
      "label": "ABS required on trailers and converter dollies",
      "value": "Built on or after March 1, 1998",
      "section": "6.3.1 – Trailers Required to Have ABS",
      "page": 87
    },
    {
      "key": "fifth-wheel-space",
      "label": "Space between the upper and lower fifth wheel",
      "value": "No space at all",
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "page": 89
    }
  ],
  "questions": [
    {
      "id": "combination-vehicles-001",
      "number": 1,
      "section": "6.1.1 – Rollover Risks",
      "stem": "How much more likely is a fully loaded rig to roll over in a crash than an empty rig?",
      "choices": [
        "Ten times more likely",
        "Twice as likely",
        "About the same",
        "Ten percent more likely"
      ],
      "answer": 0,
      "explanation": "More than half of truck driver deaths in crashes are the result of rollovers, and fully loaded rigs are ten times more likely to roll over than empty rigs.",
      "source": {
        "section": "6.1.1 – Rollover Risks",
        "page": 82,
        "printedPage": "6-1",
        "fact": "rollover-risk"
      }
    },
    {
      "id": "combination-vehicles-002",
      "number": 2,
      "section": "6.1.1 – Rollover Risks",
      "stem": "Which two things help prevent a rollover in a combination vehicle?",
      "choices": [
        "Keep cargo as close to the ground as possible and drive slowly around turns",
        "Load cargo high and brake late",
        "Keep the trailer empty and drive fast",
        "Add weight to the top of the trailer and use the retarder"
      ],
      "answer": 0,
      "explanation": "Keep the cargo as close to the ground as possible and drive slowly around corners, ramps, and off ramps to prevent rollover.",
      "source": {
        "section": "6.1.1 – Rollover Risks",
        "page": 82,
        "printedPage": "6-1"
      }
    },
    {
      "id": "combination-vehicles-003",
      "number": 3,
      "section": "6.1.2 – Steer Gently",
      "stem": "What does a rearward amplification of 3.5 for triples mean?",
      "choices": [
        "The last trailer can be rolled 3.5 times as easily as a five-axle tractor",
        "The rig is 3.5 feet longer than a five-axle tractor",
        "The rig stops 3.5 times faster",
        "The tractor weighs 3.5 times more"
      ],
      "answer": 0,
      "explanation": "Rearward amplification of 3.5 for triples means you can roll the last trailer of triples 3.5 times as easily as a five-axle tractor.",
      "source": {
        "section": "6.1.2 – Steer Gently",
        "page": 82,
        "printedPage": "6-1",
        "fact": "amplification"
      }
    },
    {
      "id": "combination-vehicles-004",
      "number": 4,
      "section": "6.1.2 – Steer Gently",
      "stem": "Why must you steer gently and smoothly when pulling trailers?",
      "choices": [
        "A sudden movement can cause the crack-the-whip effect and tip the trailer over",
        "It saves fuel on long trips",
        "It keeps the engine rpm low",
        "It keeps the air tanks charged"
      ],
      "answer": 0,
      "explanation": "Trucks with trailers have a dangerous crack-the-whip effect, and a quick lane change can turn the trailer over, so steer gently and smoothly.",
      "source": {
        "section": "6.1.2 – Steer Gently",
        "page": 82,
        "printedPage": "6-1"
      }
    },
    {
      "id": "combination-vehicles-005",
      "number": 5,
      "section": "6.1.3 – Brake Early",
      "stem": "How does an empty combination vehicle compare with a fully loaded one when stopping?",
      "choices": [
        "It takes longer to stop when empty than when fully loaded",
        "It always stops in a shorter distance",
        "The stopping distance does not change",
        "Only the trailer brakes are used when empty"
      ],
      "answer": 0,
      "explanation": "Large combination vehicles take longer to stop when they are empty than when they are fully loaded, because stiff springs and strong brakes give poor traction.",
      "source": {
        "section": "6.1.3 – Brake Early",
        "page": 82,
        "printedPage": "6-1"
      }
    },
    {
      "id": "combination-vehicles-006",
      "number": 6,
      "section": "6.1.5 – Prevent Trailer Skids",
      "stem": "When is a trailer jackknife most likely to happen?",
      "choices": [
        "When the trailer is empty or lightly loaded",
        "When the trailer is fully loaded",
        "Only on dry pavement",
        "Only when the trailer has spring brakes"
      ],
      "answer": 0,
      "explanation": "When the wheels of a trailer lock up, the trailer tends to swing around, and this is more likely when the trailer is empty or lightly loaded.",
      "source": {
        "section": "6.1.5 – Prevent Trailer Skids",
        "page": 83,
        "printedPage": "6-2"
      }
    },
    {
      "id": "combination-vehicles-007",
      "number": 7,
      "section": "6.1.5 – Prevent Trailer Skids",
      "stem": "What is the earliest and best way to recognize that the trailer has started to skid?",
      "choices": [
        "See it in your mirrors",
        "Feel the steering wheel vibrate",
        "Hear the tires squeal",
        "Watch the air pressure gauge"
      ],
      "answer": 0,
      "explanation": "The earliest and best way to recognize that the trailer has started to skid is by seeing it in your mirrors, so check them any time you brake hard.",
      "source": {
        "section": "6.1.5 – Prevent Trailer Skids",
        "page": 83,
        "printedPage": "6-2"
      }
    },
    {
      "id": "combination-vehicles-008",
      "number": 8,
      "section": "6.1.5 – Prevent Trailer Skids",
      "stem": "How should you stop a trailer skid?",
      "choices": [
        "Release the brakes to get traction back",
        "Use the trailer hand brake to straighten the rig",
        "Brake harder and steer into the skid",
        "Accelerate until the trailer grips"
      ],
      "answer": 0,
      "explanation": "Release the brakes to get traction back; do not use the trailer hand brake to straighten the rig, because the trailer brakes caused the skid in the first place.",
      "source": {
        "section": "6.1.5 – Prevent Trailer Skids",
        "page": 84,
        "printedPage": "6-3"
      }
    },
    {
      "id": "combination-vehicles-009",
      "number": 9,
      "section": "6.1.6 – Turn Wide",
      "stem": "What is off-tracking?",
      "choices": [
        "The rear wheels following a different path than the front wheels",
        "The trailer braking later than the tractor",
        "The tractor pulling to the right on a grade",
        "The air lines rubbing on the frame"
      ],
      "answer": 0,
      "explanation": "Off-tracking, or cheating, is when the rear wheels follow a different path than the front wheels, and longer vehicles off-track more.",
      "source": {
        "section": "6.1.6 – Turn Wide",
        "page": 84,
        "printedPage": "6-3"
      }
    },
    {
      "id": "combination-vehicles-010",
      "number": 10,
      "section": "6.1.6 – Turn Wide",
      "stem": "If you cannot complete a right turn without entering another lane, when should you turn wide?",
      "choices": [
        "As you complete the turn, keeping the rear of the vehicle close to the curb",
        "Before starting the turn by swinging left",
        "In the middle of the turn while stopping",
        "After crossing the curb"
      ],
      "answer": 0,
      "explanation": "Turn wide as you complete the turn rather than swinging wide to the left before starting, because that keeps other drivers from passing you on the right.",
      "source": {
        "section": "6.1.6 – Turn Wide",
        "page": 84,
        "printedPage": "6-3"
      }
    },
    {
      "id": "combination-vehicles-011",
      "number": 11,
      "section": "6.1.7 – Backing with a Trailer",
      "stem": "When backing a trailer, which way do you turn the steering wheel?",
      "choices": [
        "In the opposite direction from where you want the trailer to go",
        "In the same direction you want the trailer to go",
        "Only toward the driver's side",
        "It depends on the trailer weight"
      ],
      "answer": 0,
      "explanation": "When backing a trailer, you turn the steering wheel in the opposite direction, and once the trailer starts to turn you must turn the wheel the other way to follow it.",
      "source": {
        "section": "6.1.7 – Backing with a Trailer",
        "page": 84,
        "printedPage": "6-3"
      }
    },
    {
      "id": "combination-vehicles-012",
      "number": 12,
      "section": "6.2.1 – Trailer Hand Valve",
      "stem": "When should you use the trailer hand valve?",
      "choices": [
        "Only to test the trailer brakes",
        "Whenever you slow for traffic",
        "To hold the rig on a hill",
        "To straighten a jackknifing trailer"
      ],
      "answer": 0,
      "explanation": "The trailer hand valve works the trailer brakes and should be used only to test the trailer brakes, not in driving, because it can make the trailer skid.",
      "source": {
        "section": "6.2.1 – Trailer Hand Valve",
        "page": 85,
        "printedPage": "6-4"
      }
    },
    {
      "id": "combination-vehicles-013",
      "number": 13,
      "section": "6.2.1 – Trailer Hand Valve",
      "stem": "Why should you never use the trailer hand valve for parking?",
      "choices": [
        "All the air might leak out and unlock the brakes",
        "It is too hard to reach from the cab",
        "It will damage the glad hands",
        "The trailer service brakes will overheat"
      ],
      "answer": 0,
      "explanation": "Never use the hand valve for parking because all the air might leak out and unlock the brakes on trailers that do not have spring brakes; use the parking brakes or chocks.",
      "source": {
        "section": "6.2.1 – Trailer Hand Valve",
        "page": 85,
        "printedPage": "6-4"
      }
    },
    {
      "id": "combination-vehicles-014",
      "number": 14,
      "section": "6.2.2 – Tractor Protection Valve",
      "stem": "What does the tractor protection valve do?",
      "choices": [
        "It keeps air in the tractor brake system if the trailer breaks away or develops a leak",
        "It increases the trailer brake pressure",
        "It drains water from the air tanks",
        "It releases the trailer spring brakes"
      ],
      "answer": 0,
      "explanation": "The tractor protection valve keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak.",
      "source": {
        "section": "6.2.2 – Tractor Protection Valve",
        "page": 86,
        "printedPage": "6-5"
      }
    },
    {
      "id": "combination-vehicles-015",
      "number": 15,
      "section": "6.2.2 – Tractor Protection Valve",
      "stem": "At what pressure does the tractor protection valve close automatically?",
      "choices": [
        "20 to 45 psi",
        "55 to 70 psi",
        "85 to 100 psi",
        "120 to 140 psi"
      ],
      "answer": 0,
      "explanation": "The tractor protection valve closes automatically if air pressure is low, in the range of 20 to 45 psi, which puts on the trailer emergency brakes.",
      "source": {
        "section": "6.2.2 – Tractor Protection Valve",
        "page": 86,
        "printedPage": "6-5",
        "fact": "tractor-protection"
      }
    },
    {
      "id": "combination-vehicles-016",
      "number": 16,
      "section": "6.2.3 – Trailer Air Supply Control",
      "stem": "What does pushing in the trailer air supply control do?",
      "choices": [
        "Supplies the trailer with air",
        "Puts on the trailer emergency brakes",
        "Drains the trailer air tanks",
        "Closes the tractor protection valve"
      ],
      "answer": 0,
      "explanation": "On newer vehicles the trailer air supply control is a red eight-sided knob; push it in to supply the trailer with air and pull it out to shut the air off and put on the trailer emergency brakes.",
      "source": {
        "section": "6.2.3 – Trailer Air Supply Control",
        "page": 86,
        "printedPage": "6-5"
      }
    },
    {
      "id": "combination-vehicles-017",
      "number": 17,
      "section": "6.2.4 – Trailer Air-lines",
      "stem": "What are the two air-lines on every combination vehicle?",
      "choices": [
        "The service line and the emergency line",
        "The primary line and the secondary line",
        "The red line and the green line",
        "The front line and the rear line"
      ],
      "answer": 0,
      "explanation": "Every combination vehicle has two air-lines, the service line and the emergency line, running between each vehicle.",
      "source": {
        "section": "6.2.4 – Trailer Air-lines",
        "page": 86,
        "printedPage": "6-5"
      }
    },
    {
      "id": "combination-vehicles-018",
      "number": 18,
      "section": "6.2.4 – Trailer Air-lines",
      "stem": "What does the service air-line do?",
      "choices": [
        "It carries air controlled by the foot brake or trailer hand brake",
        "It charges the trailer air tanks",
        "It controls the trailer emergency brakes",
        "It carries electricity to the trailer"
      ],
      "answer": 0,
      "explanation": "The service line, also called the control or signal line, carries air controlled by the foot brake or the trailer hand brake and is connected to relay valves.",
      "source": {
        "section": "6.2.4 – Trailer Air-lines",
        "page": 86,
        "printedPage": "6-5"
      }
    },
    {
      "id": "combination-vehicles-019",
      "number": 19,
      "section": "6.2.4 – Trailer Air-lines",
      "stem": "What are the two purposes of the emergency air-line?",
      "choices": [
        "It supplies air to the trailer air tanks and controls the trailer emergency brakes",
        "It supplies the trailer lights and the horn",
        "It charges the tractor air tanks and the tires",
        "It controls the service brakes and the parking brake"
      ],
      "answer": 0,
      "explanation": "The emergency line, also called the supply line, supplies air to the trailer air tanks and controls the emergency brakes on combination vehicles.",
      "source": {
        "section": "6.2.4 – Trailer Air-lines",
        "page": 86,
        "printedPage": "6-5"
      }
    },
    {
      "id": "combination-vehicles-020",
      "number": 20,
      "section": "6.2.4 – Trailer Air-lines",
      "stem": "Which colors are commonly used for the service and emergency air-lines?",
      "choices": [
        "Blue for service and red for emergency",
        "Red for service and blue for emergency",
        "Green for service and yellow for emergency",
        "Black for service and white for emergency"
      ],
      "answer": 0,
      "explanation": "Colors are sometimes used to avoid mistakes: blue is used for the service lines and red for the emergency supply lines.",
      "source": {
        "section": "6.2.4 – Trailer Air-lines",
        "page": 86,
        "printedPage": "6-5",
        "fact": "air-line-colors"
      }
    },
    {
      "id": "combination-vehicles-021",
      "number": 21,
      "section": "6.2.5 – Hose Couplers (Glad Hands)",
      "stem": "How should you connect glad hands?",
      "choices": [
        "Press the two seals together with the couplers at a 90 degree angle and turn to lock",
        "Push them straight together until they click",
        "Twist them apart before connecting",
        "Connect them with the engine running"
      ],
      "answer": 0,
      "explanation": "Clean the couplers and rubber seals, press the seals together with the couplers at a 90 degree angle to each other, and turn to join and lock them.",
      "source": {
        "section": "6.2.5 – Hose Couplers (Glad Hands)",
        "page": 86,
        "printedPage": "6-5"
      }
    },
    {
      "id": "combination-vehicles-022",
      "number": 22,
      "section": "6.2.7 – Shut-off Valves",
      "stem": "Which shut-off valves should be closed on a combination vehicle?",
      "choices": [
        "Only the valves at the back of the last trailer",
        "All valves on every trailer",
        "The valves at the front of the first trailer",
        "No valves should ever be closed"
      ],
      "answer": 0,
      "explanation": "All shut-off valves must be open except the ones at the back of the last trailer, which must be closed.",
      "source": {
        "section": "6.2.7 – Shut-off Valves",
        "page": 87,
        "printedPage": "6-6",
        "fact": "shutoff-valves"
      }
    },
    {
      "id": "combination-vehicles-023",
      "number": 23,
      "section": "6.2.8 – Trailer Service, Parking and Emergency Brakes",
      "stem": "Why must you use wheel chocks when you park a trailer that has no spring brakes?",
      "choices": [
        "The emergency brakes hold only as long as air remains in the trailer air tank",
        "The brakes are too strong for the trailer",
        "The brakes apply only when the engine runs",
        "The trailer has no brakes at all"
      ],
      "answer": 0,
      "explanation": "Trailers without spring brakes have emergency brakes that work from air stored in the trailer air tank; when the air leaks away there are no brakes, so use wheel chocks.",
      "source": {
        "section": "6.2.8 – Trailer Service, Parking and Emergency Brakes",
        "page": 87,
        "printedPage": "6-6"
      }
    },
    {
      "id": "combination-vehicles-024",
      "number": 24,
      "section": "6.3.1 – Trailers Required to Have ABS",
      "stem": "Which trailers and converter dollies are required to have ABS?",
      "choices": [
        "Those built on or after March 1, 1998",
        "Those built on or after March 1, 1997",
        "All trailers regardless of age",
        "Only trailers over 10,000 pounds"
      ],
      "answer": 0,
      "explanation": "All trailers and converter dollies built on or after March 1, 1998 are required to have ABS, though many older ones were voluntarily equipped.",
      "source": {
        "section": "6.3.1 – Trailers Required to Have ABS",
        "page": 87,
        "printedPage": "6-6",
        "fact": "abs-trailer-date"
      }
    },
    {
      "id": "combination-vehicles-025",
      "number": 25,
      "section": "6.3.2 – Braking with ABS",
      "stem": "How much control do you gain if only the trailer has ABS?",
      "choices": [
        "You still get more control and the trailer is less likely to swing out",
        "No control at all, because the tractor has no ABS",
        "Control only when the trailer is empty",
        "Control only on dry pavement"
      ],
      "answer": 0,
      "explanation": "Having ABS on only the trailer, or even on only one axle, still gives you more control over the vehicle during braking.",
      "source": {
        "section": "6.3.2 – Braking with ABS",
        "page": 88,
        "printedPage": "6-7"
      }
    },
    {
      "id": "combination-vehicles-026",
      "number": 26,
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "stem": "When inspecting the fifth wheel before coupling, how should the wheel be positioned?",
      "choices": [
        "Tilted down toward the rear of the tractor, with the jaws open",
        "Tilted up toward the cab, with the jaws closed",
        "Flat and greased only on the edges",
        "Removed from the frame"
      ],
      "answer": 0,
      "explanation": "Check that the fifth wheel is in proper position for coupling: wheel tilted down toward the rear of the tractor, jaws open, and safety unlocking handle in the automatic lock position.",
      "source": {
        "section": "6.4.1 – Coupling Tractor-Semitrailers",
        "page": 88,
        "printedPage": "6-7"
      }
    },
    {
      "id": "combination-vehicles-027",
      "number": 27,
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "stem": "Why should you never back under the trailer at an angle?",
      "choices": [
        "You might push the trailer sideways and break the landing gear",
        "The tractor mirrors will not show the trailer",
        "The fifth wheel grease will rub off",
        "The trailer brakes will release"
      ],
      "answer": 0,
      "explanation": "Put the tractor directly in front of the trailer; never back under at an angle because you might push the trailer sideways and break the landing gear.",
      "source": {
        "section": "6.4.1 – Coupling Tractor-Semitrailers",
        "page": 89,
        "printedPage": "6-8"
      }
    },
    {
      "id": "combination-vehicles-028",
      "number": 28,
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "stem": "How do you know the trailer height is correct before coupling?",
      "choices": [
        "The trailer is low enough to be raised slightly by the tractor when backed under",
        "The trailer is high enough to clear the fifth wheel completely",
        "The landing gear is off the ground",
        "The kingpin touches the bumper"
      ],
      "answer": 0,
      "explanation": "The trailer should be low enough that it is raised slightly by the tractor when the tractor is backed under it; if it is too low the tractor may damage the nose, and if too high it may not couple.",
      "source": {
        "section": "6.4.1 – Coupling Tractor-Semitrailers",
        "page": 89,
        "printedPage": "6-8"
      }
    },
    {
      "id": "combination-vehicles-029",
      "number": 29,
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "stem": "After coupling, how much space should there be between the upper and lower fifth wheel?",
      "choices": [
        "No space at all",
        "About half an inch",
        "At least two inches",
        "It does not matter if the kingpin is covered"
      ],
      "answer": 0,
      "explanation": "Make sure there is no space between the upper and lower fifth wheel; if there is space, the kingpin may be on top of the closed fifth wheel jaws and the trailer could come loose.",
      "source": {
        "section": "6.4.1 – Coupling Tractor-Semitrailers",
        "page": 89,
        "printedPage": "6-8",
        "fact": "fifth-wheel-space"
      }
    },
    {
      "id": "combination-vehicles-030",
      "number": 30,
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "stem": "How do you check that the trailer is locked onto the tractor after coupling?",
      "choices": [
        "Raise the landing gear slightly and pull gently forward with the trailer brakes locked",
        "Shake the trailer by hand",
        "Sound the horn and watch the mirrors",
        "Release the trailer brakes and drive forward"
      ],
      "answer": 0,
      "explanation": "Raise the trailer landing gear slightly off the ground and pull the tractor gently forward while the trailer brakes are still locked to check that the trailer is locked onto the tractor.",
      "source": {
        "section": "6.4.1 – Coupling Tractor-Semitrailers",
        "page": 89,
        "printedPage": "6-8"
      }
    },
    {
      "id": "combination-vehicles-031",
      "number": 31,
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "stem": "When you inspect the coupling by looking into the back of the fifth wheel, what should the jaws be around?",
      "choices": [
        "The shank of the kingpin",
        "The head of the kingpin",
        "The release arm",
        "The glad hand"
      ],
      "answer": 0,
      "explanation": "Look into the back of the fifth wheel and make sure the jaws have closed around the shank of the kingpin, not the head.",
      "source": {
        "section": "6.4.1 – Coupling Tractor-Semitrailers",
        "page": 89,
        "printedPage": "6-8"
      }
    },
    {
      "id": "combination-vehicles-032",
      "number": 32,
      "section": "6.4.1 – Coupling Tractor-Semitrailers",
      "stem": "How far should you raise the landing gear after coupling?",
      "choices": [
        "All the way up, and secure the crank handle",
        "Until it just clears the ground by an inch",
        "Half way, to save time",
        "Only if the trailer is empty"
      ],
      "answer": 0,
      "explanation": "Raise the landing gear all the way up and secure the crank handle; never drive with the landing gear only part way up, because it may catch on railroad tracks or other things.",
      "source": {
        "section": "6.4.1 – Coupling Tractor-Semitrailers",
        "page": 90,
        "printedPage": "6-9"
      }
    },
    {
      "id": "combination-vehicles-033",
      "number": 33,
      "section": "6.4.2 – Uncoupling Tractor-Semitrailers",
      "stem": "How do you ease the pressure on the fifth wheel locking jaws before uncoupling?",
      "choices": [
        "Shut off the trailer air supply to lock the trailer brakes and back up gently",
        "Pull the release handle to open while rolling",
        "Apply the tractor parking brake and drive forward",
        "Release the trailer brakes and coast"
      ],
      "answer": 0,
      "explanation": "Shut off the trailer air supply to lock the trailer brakes, then ease pressure on the fifth wheel locking jaws by backing up gently to help release the locking lever.",
      "source": {
        "section": "6.4.2 – Uncoupling Tractor-Semitrailers",
        "page": 90,
        "printedPage": "6-9"
      }
    },
    {
      "id": "combination-vehicles-034",
      "number": 34,
      "section": "6.4.2 – Uncoupling Tractor-Semitrailers",
      "stem": "How much should you turn the landing gear crank on a loaded trailer?",
      "choices": [
        "A few extra turns after firm contact to lift some weight, but not off the fifth wheel",
        "All the way down until the trailer is off the fifth wheel",
        "Only until it touches the ground",
        "No extra turns are needed"
      ],
      "answer": 0,
      "explanation": "If the trailer is loaded, after the landing gear makes firm contact with the ground, turn the crank a few extra turns to lift some weight off the tractor, but do not lift the trailer off the fifth wheel.",
      "source": {
        "section": "6.4.2 – Uncoupling Tractor-Semitrailers",
        "page": 90,
        "printedPage": "6-9"
      }
    },
    {
      "id": "combination-vehicles-035",
      "number": 35,
      "section": "6.4.2 – Uncoupling Tractor-Semitrailers",
      "stem": "What should you do with the air-lines and electrical cable after uncoupling?",
      "choices": [
        "Connect the glad hands to dummy couplers and hang the electrical plug down",
        "Leave them on the ground for the next driver",
        "Tie them to the trailer bumper",
        "Plug them into each other and leave them hanging"
      ],
      "answer": 0,
      "explanation": "Connect the air-line glad hands to dummy couplers or couple them together, and hang the electrical cable with the plug down to prevent moisture from entering it.",
      "source": {
        "section": "6.4.2 – Uncoupling Tractor-Semitrailers",
        "page": 90,
        "printedPage": "6-9"
      }
    },
    {
      "id": "combination-vehicles-036",
      "number": 36,
      "section": "6.5.1 – Additional Things to Check during a Walk-around Inspection",
      "stem": "Why should the fifth wheel not be too far forward?",
      "choices": [
        "The tractor frame could hit the landing gear or the cab could hit the trailer during turns",
        "The trailer would be too light on the drive axles",
        "The air lines would be too short",
        "The kingpin would not lock"
      ],
      "answer": 0,
      "explanation": "Check that the fifth wheel is not so far forward that the tractor frame will hit the landing gear, or the cab hit the trailer, during turns.",
      "source": {
        "section": "6.5.1 – Additional Things to Check during a Walk-around Inspection",
        "page": 94,
        "printedPage": "6-13"
      }
    },
    {
      "id": "combination-vehicles-037",
      "number": 37,
      "section": "6.5.2 – Combination Vehicle Brake Check",
      "stem": "How do you check that air flows to all trailers?",
      "choices": [
        "Open the emergency line shut-off at the rear of the last trailer and listen for escaping air",
        "Apply the parking brake and watch the gauge",
        "Pull the trailer air supply knob and count to ten",
        "Press the foot brake and check the lights"
      ],
      "answer": 0,
      "explanation": "Open the emergency line shut-off valve at the rear of the last trailer; you should hear air escaping, showing the entire system is charged.",
      "source": {
        "section": "6.5.2 – Combination Vehicle Brake Check",
        "page": 94,
        "printedPage": "6-13"
      }
    },
    {
      "id": "combination-vehicles-038",
      "number": 38,
      "section": "6.5.2 – Combination Vehicle Brake Check",
      "stem": "How do you test the tractor protection valve?",
      "choices": [
        "Reduce the air pressure and check that the trailer air supply control pops out at 20 to 45 psi",
        "Pull the knob out and check the gauge rises",
        "Open the drain valves and listen",
        "Press the hand valve and release it"
      ],
      "answer": 0,
      "explanation": "With the system charged and the engine off, step on and off the brake pedal to reduce pressure; the trailer air supply control should pop out, usually within 20 to 45 psi.",
      "source": {
        "section": "6.5.2 – Combination Vehicle Brake Check",
        "page": 94,
        "printedPage": "6-13"
      }
    },
    {
      "id": "combination-vehicles-039",
      "number": 39,
      "section": "6.5.2 – Combination Vehicle Brake Check",
      "stem": "How do you test the trailer emergency brakes?",
      "choices": [
        "Charge the system, pull out the trailer air supply control, and pull gently with the tractor",
        "Drive forward at 20 mph and pull the hand valve",
        "Open the shut-off valves at the rear of the last trailer",
        "Press the foot brake and watch the trailer lights"
      ],
      "answer": 0,
      "explanation": "Charge the trailer air brake system and check that the trailer rolls freely, then pull out the trailer air supply control and pull gently with the tractor to check the emergency brakes are on.",
      "source": {
        "section": "6.5.2 – Combination Vehicle Brake Check",
        "page": 95,
        "printedPage": "6-14"
      }
    },
    {
      "id": "combination-vehicles-040",
      "number": 40,
      "section": "6.5.2 – Combination Vehicle Brake Check",
      "stem": "How do you test the trailer service brakes?",
      "choices": [
        "Move forward slowly and apply the trailer brakes with the hand control",
        "Pull the air supply knob and listen for air",
        "Press the foot brake and check the gauge",
        "Open the emergency line shut-off and listen"
      ],
      "answer": 0,
      "explanation": "With normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply the trailer brakes with the hand control, if so equipped; you should feel the brakes come on.",
      "source": {
        "section": "6.5.2 – Combination Vehicle Brake Check",
        "page": 95,
        "printedPage": "6-14"
      }
    }
  ]
}