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Combination Vehicles Flashcards

20 cards from real CDL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 20 Combination Vehicles flashcards as text

  1. THERE ARE TWO THINGS THAT A DRIVER CAN DO TO PREVENT A ROLLOVER. THEY ARE "GO SLOW AROUND CORNERS" AND _____.

    Answer: Keep the weight of your cargo as close to the ground as possible

    Rollovers occur when a vehicle's center of gravity shifts too far, often due to excessive speed in turns or sudden maneuvers. Keeping the cargo weight as low as possible significantly lowers the vehicle's center of gravity, increasing its stability and reducing the likelihood of tipping. Combining this with reducing speed around corners are two crucial strategies for preventing dangerous rollover accidents.

  2. WHY SHOULD YOU NOT USE THE TRAILER HAND VALVE WHILE DRIVING?

    Answer: Because of the danger of making the trailer skid

    Using the trailer hand valve while driving applies only the trailer brakes, which can cause the trailer wheels to lock up and skid, especially in slippery conditions. A skidding trailer can lead to a jackknife, where the trailer swings out and pushes the tractor, resulting in a severe loss of control. The foot brake, by contrast, applies brakes to both the tractor and trailer proportionally, maintaining stability.

  3. WHEN YOU BACK A TRAILER, YOU SHOULD POSITION YOUR VEHICLE SO YOU CAN BACK IN A CURVED PATH TO THE DRIVER’S SIDE. TRUE OR FALSE?

    Answer: TRUE

    This statement is TRUE. When backing a trailer, positioning your vehicle to back towards the driver's side (left side) provides significantly better visibility through your side mirror. This enhanced view allows for more precise control over the trailer's path and helps the driver monitor surroundings more effectively. Backing to the passenger side severely limits visibility and increases the risk of errors or collisions.

  4. WHAT MIGHT HAPPEN IF THE TRAILER IS TOO HIGH WHEN YOU TRY TO COUPLE?

    Answer: The trailer may not couple correctly

    If the trailer is too high during coupling, the kingpin may not properly enter the fifth wheel's locking jaws, or the jaws may not fully close around the kingpin's shank. This can result in a 'high hook,' where the trailer is not securely attached to the tractor. A high hook is extremely dangerous as the trailer could separate from the tractor during transit, leading to a catastrophic accident.

  5. YOU ARE DRIVING A SEMI AND THE TRAILER BREAKS AWAY, PULLING APART THE AIR LINES. YOU EXPECT THE TRAILER BRAKES TO COME ON AND ____ .

    Answer: The tractor brakes to keep working

    In a trailer breakaway scenario, where the air lines separate, the emergency air line losing pressure will automatically activate the trailer's emergency brakes, bringing the trailer to a stop. Crucially, the tractor's air brake system is designed to remain fully operational. This allows the driver to maintain control of the tractor and bring it to a safe, controlled stop independently, preventing further danger.

  6. WHICH SHUT-OFF VALVES SHOULD BE OPEN AND WHICH CLOSED?

    Answer: Emergency and service lines at the back of the last trailer closed, valves on the trailer open

    For a combination vehicle, the shut-off valves at the very back of the last trailer must be closed to prevent air from escaping the system. All other shut-off valves on the trailer, which connect the tractor to the trailer or between multiple trailers, should be open. This configuration ensures that air flows correctly throughout the entire brake system, providing proper pressure to all brakes for safe operation.

  7. THE AIR LEAKAGE RATE FOR A COMBINATION VEHICLE (ENGINE OFF, BRAKES OFF) SHOULD BE NO MORE THAN ____ PSI PER MINUTE.

    Answer: 3

    For a combination vehicle, the maximum allowable air leakage rate with the engine off and brakes off is 3 PSI per minute. This standard ensures the air brake system is sufficiently airtight to maintain proper pressure for safe and effective braking. A leakage rate higher than 3 PSI per minute indicates a problem that must be identified and repaired before the vehicle can be safely operated.

  8. THE FEWER AXLES ON A UNIT, THE MORE STABLE IT IS?

    Answer: FALSE

    This statement is FALSE. Generally, a unit with more axles tends to be more stable because the weight is distributed over a larger area and more points of contact with the road. This reduces the load on individual tires and axles, improving overall handling and reducing the risk of instability, especially with heavy or uneven loads. Fewer axles can concentrate weight, potentially making the vehicle less stable.

  9. AIR LINES ON A COMBINATION VEHICLE ARE OFTEN COLORED TO KEEP THEM FROM GETTING MIXED UP. THE EMERGENCY LINE IS ____; THE SERVICE LINE IS ____.

    Answer: Red, blue

    To prevent confusion and ensure correct connections, air lines on combination vehicles are color-coded. The emergency (supply) line, which provides air to the trailer's air tanks and controls the emergency brakes, is always red. The service (control) line, which applies and releases the trailer's service brakes, is always blue, allowing drivers to quickly identify and connect them correctly.

  10. WHAT IS OFF-TRACKING?

    Answer: When a vehicle goes around a corner, the rear wheels follow a different path than the front wheels

    Off-tracking, also known as 'cut-in,' describes the phenomenon where the rear wheels of a long vehicle or combination vehicle follow a different, shorter path than the front wheels when turning. This means the rear of the vehicle tracks closer to the inside of the turn. Drivers must account for off-tracking by swinging wide to prevent the rear of their vehicle from hitting curbs, signs, or other objects.

  11. COMBINATION VEHICLES ARE USUALLY HEAVIER, LONGER, AND REQUIRE MORE DRIVING SKILL THAN SINGLE COMMERCIAL VEHICLES.

    Answer: TRUE

    This statement is TRUE. Combination vehicles, such as tractor-trailers, are inherently more complex to operate due to their increased length, greater weight, and multiple pivot points. They demand superior driving skills for maneuvering, backing, braking, and managing off-tracking compared to single commercial vehicles. This complexity is why specific CDL endorsements are required for their operation.

  12. HOW CAN YOU TEST THE TRAILER EMERGENCY BRAKES?

    Answer: Place the tractor emergency valve in the emergency position, try to nudge the vehicle forward

    To test the trailer emergency brakes, first ensure your air tanks are fully charged. Then, pull out the trailer air supply (emergency) valve, which should cause the trailer's emergency brakes to apply. With the trailer brakes engaged, gently try to pull the vehicle forward with the tractor. If the trailer brakes are working correctly, they will hold the trailer firmly in place, preventing it from moving.

  13. THE SAFETY LATCH FOR THE FIFTH WHEEL LOCKING LEVER MUST BE ____ FOR A COUPLING TO BE COMPLETE

    Answer: Over the locking lever

    For a secure coupling, the fifth wheel locking lever must be fully closed around the kingpin, and the safety latch must be positioned over the locking lever. This critical step ensures that the locking lever cannot accidentally open during transit, which would lead to the dangerous detachment of the trailer from the tractor. Always verify the safety latch is correctly engaged after coupling.

  14. WHAT TYPE OF TRAILERS CAN GET STUCK ON RAILROAD-HIGHWAY CROSSINGS?

    Answer: Low slung units and single-axle tractor pulling a long trailer with its landing gear set to accommodate a tandem-axle tractor

    Low slung units and single-axle tractors pulling long trailers are particularly vulnerable to getting stuck on railroad-highway crossings. This risk is heightened if the trailer's landing gear is set to accommodate a tandem-axle tractor, which can make the front of the trailer too low for a single-axle tractor. The varying angles of railroad crossings can cause these vehicles to high-center, blocking the tracks and creating a severe hazard.

  15. TRAILER MADE BEFORE 1975, EQUIPPED WITH AIR BRAKES:

    Answer: Often do not have spring brakes

    Trailers manufactured before 1975, even if equipped with air brakes, often lack spring brakes as a standard feature. Spring brakes automatically apply when air pressure is lost, serving as both an emergency and parking brake. Drivers operating older trailers must be aware that their emergency braking system might rely solely on air pressure, which can be lost, requiring different safety considerations.

  16. WHAT PART OF THE KINGPIN SHOULD THE LOCKING JAWS CLOSE AROUND?

    Answer: The shank

    The locking jaws of the fifth wheel are specifically designed to close securely around the shank (the cylindrical part) of the kingpin, just below its head. This ensures a tight and safe connection between the tractor and trailer. If the jaws do not properly engage the shank, the coupling is not secure, and the trailer could detach, leading to a dangerous situation.

  17. THERE ARE TWO THINGS THAT A DRIVER CAN DO TO PREVENT A ROLLOVER. THEY ARE "GO SLOW AROUND CORNERS" AND _____.

    Answer: Keep the weight of your cargo as close to the ground as possible

    Rollovers occur when a vehicle's center of gravity shifts too far, often due to excessive speed in turns or sudden maneuvers. Keeping the cargo weight as low as possible significantly lowers the vehicle's center of gravity, increasing its stability and reducing the likelihood of tipping. Combining this with reducing speed around corners are two crucial strategies for preventing dangerous rollover accidents.

  18. YOU ARE DRIVING A SEMI AND THE TRAILER BREAKS AWAY, PULLING APART THE AIR LINES. YOU EXPECT THE TRAILER BRAKES TO COME ON AND ____ .

    Answer: The tractor brakes to keep working

    In a trailer breakaway scenario, where the air lines separate, the emergency air line losing pressure will automatically activate the trailer's emergency brakes, bringing the trailer to a stop. Crucially, the tractor's air brake system is designed to remain fully operational. This allows the driver to maintain control of the tractor and bring it to a safe, controlled stop independently, preventing further danger.

  19. COMBINATION VEHICLES ARE USUALLY HEAVIER, LONGER, AND REQUIRE MORE DRIVING SKILL THAN SINGLE COMMERCIAL VEHICLES.

    Answer: TRUE

    This statement is TRUE. Combination vehicles, such as tractor-trailers, are inherently more complex to operate due to their increased length, greater weight, and multiple pivot points. They demand superior driving skills for maneuvering, backing, braking, and managing off-tracking compared to single commercial vehicles. This complexity is why specific CDL endorsements are required for their operation.

  20. WHAT IS OFF-TRACKING?

    Answer: When a vehicle goes around a corner, the rear wheels follow a different path than the front wheels

    Off-tracking, also known as 'cut-in,' describes the phenomenon where the rear wheels of a long vehicle or combination vehicle follow a different, shorter path than the front wheels when turning. This means the rear of the vehicle tracks closer to the inside of the turn. Drivers must account for off-tracking by swinging wide to prevent the rear of their vehicle from hitting curbs, signs, or other objects.