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. ↗
