After a sharp evasive lane change, a semitrailer leans much more than its tractor. Which characteristic explains why the tractor remaining upright does not prove the whole rig is stable?
Correct answer: Steering effects can be amplified toward the rear of the combination.
Abrupt steering can amplify the trailer's sideways response. A trailer can roll while the tractor remains upright, so smooth steering and enough space to avoid abrupt maneuvers matter.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.2 - Steer Gently; printed 6-1, physical 87; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A driver has uncoupled the semitrailer and will drive the tractor alone. Which expectation should guide the first part of the trip?
Correct answer: A bobtail tractor can be difficult to stop smoothly, so preserve generous stopping room.
The manual warns that a bobtail tractor can be hard to stop smoothly. Do not assume removing the trailer makes braking easy or justifies less room; no fixed distance comparison is claimed for every model or condition.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.3 - Brake Early; printed 6-1, physical 87; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A long semitrailer's landing-gear setup was intended for a tandem-axle tractor, but a single-axle tractor is now assigned. Which clearance check addresses the manual's particular warning about this setup at a raised railroad crossing?
Correct answer: Clearance beneath the trailer and its landing gear over the raised crossing.
The manual identifies this tractor/trailer setup as a possible raised-crossing hang-up risk. Verify the actual rig's underside and landing-gear clearance; other visible clearances do not settle this particular concern.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.4 - Railroad-highway Crossings; printed 6-2, physical 88; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
During heavy braking on a straight road, the driver sees the semitrailer beginning to move sideways in the mirrors while the tractor still points ahead. How should that observation be interpreted?
Correct answer: As an early warning of a trailer skid and possible trailer jackknife.
A trailer's sideways movement during braking can reveal a developing skid before a full jackknife. Recognition should not wait until it leaves the lane. This question identifies the warning, not a model-independent skid-recovery sequence.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.5 - Prevent Trailer Skids; printed 6-2, physical 88; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A tractor's front wheels clear a curb during a slow corner, but the semitrailer wheels are drawing much closer to it. Which fact must the driver account for?
Correct answer: The trailer's rear wheels cut farther inside the turn than the tractor's front wheels.
Offtracking makes the trailer's rear wheels follow an inside path in a turn. Front-end clearance therefore cannot stand in for checking the trailer's swept path.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.6 - Turn Wide; Figure 6.3; printed 6-3, physical 89; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
In a controlled training area, a conventional tractor and single semitrailer begin straight and aligned. Viewed from the driver's seat, the top of the steering wheel is initially turned left while reversing. Which initial trailer response should the trainee expect?
Correct answer: The rear of the semitrailer starts toward the driver's right.
For the initial backing response of the aligned tractor-semitrailer described, steering-wheel movement and the desired trailer direction are opposite. Continuing a curved backing maneuver requires further corrections; this is not a complete maneuvering instruction.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.7 - Backing with a Trailer; Figure 6.5 on printed 6-4; printed 6-3, physical 89; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
Two safe yard setups reach the same trailer space. One allows a straight back; the other requires a long curved back. There is no operational need for the curve. Which setup should the driver prefer?
Correct answer: The setup permitting a straight back.
Position the combination for a straight back when practical. Curved backing adds alignment and visibility demands; if it is unavoidable, the manual favors the driver's side for visibility.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.7 - Backing with a Trailer; printed 6-3, physical 89; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
While backing a semitrailer slowly, a driver watches only the mirror showing the trailer side nearest the dock. What should change about the observation pattern?
Correct answer: Check both outside mirrors frequently to monitor both sides.
The combination-backing guidance calls for frequent checks of both outside mirrors. If the path is uncertain, stop and re-inspect it; one visible side is not proof that the other side remains clear.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.7 - Backing with a Trailer: Use Mirrors on Both Sides; printed 6-4, physical 90; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A trailer is getting poorly aligned with its destination during a slow back. A clear, safe forward path is available. What is an appropriate way to improve the setup?
Correct answer: Stop and use a controlled pull-up to reposition before backing again.
The manual allows pull-ups to reposition a combination when backing. Use the available safe space to correct the setup rather than persist with an increasingly poor approach.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.1.7 - Backing with a Trailer: Pull Forward; printed 6-4, physical 90; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A driver proposes leaving an air-braked tractor-semitrailer parked using only its trailer hand valve. Why is that plan unreliable?
Correct answer: Air leakage can release a pressure-held application; use the proper parking provisions.
The trailer hand valve is not a parking brake. Air can leak away, so use the equipment's parking brakes and required securement; trailers without spring brakes also need wheel chocks.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.1 - Trailer Hand Valve; printed 6-4, physical 90; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
On a conventional two-air-line tractor-semitrailer, brake-pedal pressure changes the signal sent to the trailer's relay valves. Which line carries that changing brake-application signal?
Correct answer: The service line.
The service line carries the brake-application signal. The emergency/supply line has a different role: charging the trailer reservoirs and controlling emergency-brake action.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.4 - Trailer Air-lines: Service Air-line; printed 6-5, physical 91; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A severe trailer-side air leak develops on an air-braked combination. Which protective function helps keep that failure from exhausting the tractor's air supply?
Correct answer: The tractor protection valve isolates the tractor from the trailer-side loss.
The tractor protection valve helps retain air in the tractor when a trailer breaks away or leaks badly. This is a recognition question; its operating thresholds and checks must follow the actual equipment specifications.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.2 - Tractor Protection Valve; printed 6-5, physical 91; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
After an air-line hookup, a trailer's spring brakes do not release as expected. The system has normal pressure and the supply control is in its prescribed position. Which check directly addresses possible misrouting of the air supply?
Correct answer: Verify that each service and supply hose connects to its matching trailer circuit.
Crossed lines can send supply air into the service circuit instead of charging the trailer tanks as intended. They are a possible cause to check, not the only possible fault. Do not force a trailer to move with brakes that will not release.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.5 - Hose Couplers (Glad Hands), continuation; printed 6-6, physical 92; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
The tractor's air hoses are not connected to a trailer, and the tractor is equipped with suitable dummy couplers. Why should the glad hands be stored on those couplers?
Correct answer: To keep dirt and water out of the air connections.
Dummy couplers protect disconnected air-line openings from contamination. Use the provisions designed for the equipment; the manual's possible alternative of joining couplers together is not universal.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.5 - Hose Couplers (Glad Hands), continuation; printed 6-6, physical 92; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A trailer receives a service-brake command. In the conventional air system described, where does its relay valve obtain the air it sends to the trailer's brake chambers?
Correct answer: From the trailer's own charged air reservoir.
The trailer's reservoir supplies the application air through relay valves; the service line tells those valves how much pressure to deliver. This separates the local air source from the control signal.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.6 - Trailer Air Tanks; printed 6-6, physical 92; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
An older trailer is confirmed to have no spring parking brakes; its emergency application depends on stored reservoir air. Why are wheel chocks important when that trailer is parked?
Correct answer: The stored air can leak away and stop holding the brakes applied.
On the specifically described non-spring-brake trailer, emergency braking lasts only while sufficient stored air remains. Chocks provide necessary protection against movement as that air leaks away; no manufacturing-date exemption is being tested.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.8 - Trailer Service, Parking and Emergency Brakes; printed 6-6, physical 92; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A combination's air pressure appears stable with the service brakes released. A large leak becomes evident when the driver applies them. Which conclusion is justified?
Correct answer: A service-line leak may become apparent only when that circuit is pressurized.
The manual warns that a major service-line leak may not be noticed until braking. The earlier released-brake observation is not sufficient proof that the system is sound; a large loss requires correction, not acceptance.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.2.8 - Trailer Service, Parking and Emergency Brakes; printed 6-6, physical 92; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
The semitrailer has working ABS, but the tractor has no ABS. Which limitation must the driver understand?
Correct answer: Trailer ABS does not prevent the tractor's wheels from locking or the tractor from jackknifing.
ABS on the trailer can reduce brake-induced trailer swing, but it does not equip the tractor with antilock control. The driver must understand the actual combination and its limits; this question gives no universal emergency brake-release recipe.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.3.2 - Braking with ABS; printed 6-7, physical 93; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A driver trained on one conventional fifth wheel is assigned a different low-lube design. Its maker's coupling instructions differ from the generic handbook sequence. What is the proper preparation?
Correct answer: Learn and follow the instructions for that actual coupling and tractor-trailer setup.
Section 6.4 explicitly says rigs differ. Use the actual equipment instructions and training; for example, not every fifth-wheel design is intended to lift the trailer during coupling.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4 - Coupling and Uncoupling, introduction; printed 6-7, physical 93; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. Equipment qualification: JOST LT SK37W-01 Rev.D, Operation Instructions for JSK 37UW Low Lube and 3CN Series, physical/printed 1; https://jostinternational.com/hubfs/Jost_International_April_2024/Pdf/jsk3cn-operation-instructions.pdf?hsLang=en#page=1. ↗
A conventional fifth-wheel plate requires grease under its manufacturer's instructions, but its working surface has been allowed to run dry. What handling concern can result?
Correct answer: Excess friction between tractor and trailer can interfere with steering.
Where lubrication is required, insufficient lubrication can increase friction between tractor and trailer and cause steering problems. This does not prescribe greasing low-lube liners or give a maintenance procedure for every design.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4.1 - Coupling Tractor-Semitrailers: Step 1, Inspect Fifth Wheel; printed 6-7, physical 93; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
Before coupling a conventional tractor-semitrailer, the driver finds that the trailer kingpin is visibly bent. The fifth-wheel opening is large enough to accept it. What is the sound decision?
Correct answer: Keep the unit out of service until the coupling defect is corrected.
A kingpin must not be bent or broken. Being able to fit into an opening does not establish a safe lock; do not attempt to force a defective coupling together.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4.1 - Coupling Tractor-Semitrailers: Step 1, continuation; printed 6-8, physical 94; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A conventional tractor is noticeably angled to a semitrailer before backing under it. Why does the manual call for straight alignment instead?
Correct answer: Angled contact can push the trailer sideways and damage its landing gear.
The handbook's conventional coupling sequence calls for direct alignment because angled backing can force the trailer sideways and damage the supports. Follow the actual equipment procedure rather than use impact to realign it.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4.1 - Coupling Tractor-Semitrailers: Step 3, Position Tractor; printed 6-8, physical 94; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
After a conventional fifth-wheel coupling attempt, the driver sees daylight between the mating upper and lower plates. A locking sound was heard. How should the visible gap be treated?
Correct answer: As evidence of an improper coupling that must be corrected before travel.
The mating plates should have no visible gap in the conventional coupling described. A gap can mean the kingpin is improperly positioned, including above closed jaws; sound alone does not establish a secure connection.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4.1 - Coupling Tractor-Semitrailers: Step 13, Inspect Coupling; printed 6-8, physical 94; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A tractor passes the gentle pull check prescribed for its conventional fifth wheel. The driver has not yet completed the required visual inspection. What does the pull-check result establish?
Correct answer: It is only part of verification; the specified visual lock checks are still necessary.
A pull check does not replace inspection of the actual lock and mating surfaces. Secure the vehicle as prescribed before inspecting, and follow the equipment's complete procedure; the handbook's order is not universal across manufacturers.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4.1 - Coupling Tractor-Semitrailers: Steps 11-13; Step 13 continues on printed 6-9; printed 6-8, physical 94; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. Manufacturer corroboration: JOST LT SK37W-01 Rev.D, physical/printed 2 (pull check plus visual inspection); SAF-HOLLAND ELI-te Coupling Technology, Technology Advantages (visual inspection before tug), https://safholland.com/us/en/technology/technologyCategory/fifth-wheels/eli-te-coupling-technology; both reviewed September 13, 2026. ↗
In a secured conventional fifth-wheel inspection, the lock appears to be gripping the enlarged head at the kingpin's bottom instead of the narrower shank. Which assessment is correct?
Correct answer: The engagement is wrong; the jaws must lock around the shank.
Figure 6.8 identifies the kingpin's head and shank, and the inspection text requires the jaws around the shank, not the head. A reassuring handle position does not excuse the wrong engagement.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.5.1 - Additional Things to Check during a Walk-around Inspection: Coupling System Areas; Figure 6.8; printed 6-10, physical 96; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A combination's hoses and cable look undamaged, but they are stretched nearly tight with the tractor and trailer straight. Which inspection concern remains?
Correct answer: They need enough safely supported slack for turns without snagging or contacting moving parts.
Air and electrical connections must remain protected as the rig articulates. Check adequate turning slack and secure routing together; excessive loose line near moving parts is not the solution.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.5.1 - Additional Things to Check during a Walk-around Inspection: Air and electric lines to trailer; printed 6-10, physical 96; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
On a tractor with a sliding fifth wheel, the control has been returned to its locked setting, but one locking pin is visibly not engaged. May the control position alone be accepted as proof of securement?
Correct answer: No; all required locking pins must be present and fully engaged.
The inspection requires the sliding fifth wheel's locking pins to be present and locked. A control setting is not proof that the mechanism engaged; do not travel with an unresolved slider-lock defect.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.5.1 - Additional Things to Check during a Walk-around Inspection: Sliding fifth wheel; printed 6-10, physical 96; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A semitrailer's front weight is now fully supported by the tractor, with the landing gear raised. Which additional clearance check belongs in the departure inspection?
Correct answer: Check tire-to-trailer-nose and tractor-frame-to-landing-gear clearance, including room for turns.
With the trailer supported in its travel position, verify the specified tire-to-nose and frame-to-landing-gear clearances. The rig must articulate without those components contacting one another.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4.1 - Coupling Tractor-Semitrailers: Step 15, Raise Front Trailer Supports; printed 6-9, physical 95; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A driver is choosing where to leave a semitrailer. One space appears flat, but its soft surface may not support the landing gear under the trailer's weight. Which assessment is sound?
Correct answer: Ground support must be verified; level appearance alone is not enough.
A suitable uncoupling surface must support the trailer, and its supports must be sound. Level appearance alone is not enough. This is a site-assessment question, not a sequence for releasing a trailer.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.4.2 - Uncoupling Tractor-Semitrailers: Step 1, Position Rig; support check continues on printed 6-10; printed 6-9, physical 95; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A trailer has hydraulically powered landing gear. During its secured inspection, fresh hydraulic leakage is visible even though the supports are fully raised. What conclusion is appropriate?
Correct answer: The powered landing gear still has a defect requiring attention before use.
The landing-gear inspection includes absence of air or hydraulic leakage when power-operated. The supports being raised does not cancel that condition check; follow the equipment's defect and repair procedure.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System; Section 6 - Combination Vehicles; 6.5.1 - Additional Things to Check during a Walk-around Inspection: Landing Gear, continuation; printed 6-11, physical 97; Version: July 2014. Current NCDMV-linked copy reviewed September 13, 2026. ↗
