A tractor clears a curb during a slow turn, but the trailer’s rear wheels are still approaching it. What must the driver allow for?
Correct answer: The rear wheels track inside the path of the front wheels.
Offtracking makes the trailer wheels follow a shorter, inside path. Plan a safe turn that provides room for the whole vehicle without creating a squeeze hazard.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.1.6 Turn Wide (printed 6-3); physical PDF page 87. ↗
A sudden steering move travels through a combination with several trailers. Which unit is especially vulnerable to the amplified whipping motion?
Correct answer: The last trailer.
Rearward amplification can make the last trailer move much more severely than the tractor. Smooth, planned steering reduces this rollover hazard.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.1.2 Steer Gently (printed 6-1); also 7.1.2 Beware of the Crack-the-whip Effect, physical PDF 99; physical PDF page 85. ↗
You are driving the tractor without a trailer. Should its lighter weight make you assume it will stop more quickly?
Correct answer: No; a bobtail tractor can have poor braking traction and need extra stopping room.
The manual warns that bobtail tractors can be difficult to stop smoothly. Reduced load on the drive wheels can reduce available traction.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.1.3 Brake Early (printed 6-1); physical PDF page 85. ↗
In your mirror, the trailer begins swinging sideways because its wheels have locked during braking. What helps restore its path?
Correct answer: Release the braking that locked the trailer wheels so they can regain traction.
A trailer-wheel braking skid requires the wheels to roll again to regain traction. Extra trailer braking worsens the skid.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.1.5 Prevent Trailer Skids (printed 6-3); physical PDF page 87. ↗
A driver proposes using the trailer hand valve to hold a parked rig while leaving the cab. Why is that unsafe?
Correct answer: Air can leak away and release those brakes; use the proper parking controls and secure the vehicle.
The hand valve is for testing trailer brakes, not unattended parking or ordinary driving. Air-operated service brakes may release as pressure leaks away.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.2.1 Trailer Hand Valve (printed 6-4); physical PDF page 88. ↗
A trailer air line tears apart after a breakaway. Which protection is intended to keep the leak from draining all air out of the tractor?
Correct answer: The tractor protection valve closing the air supply to the trailer.
The tractor protection valve helps preserve air in the tractor if the trailer separates or develops a major leak.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.2.2 Tractor Protection Valve (printed 6-5); physical PDF page 89. ↗
One trailer air line supplies the trailer reservoirs and controls emergency braking if its pressure is lost. Which line performs these functions?
Correct answer: The emergency or supply line.
The supply line charges trailer tanks and controls emergency braking. The service line carries the braking command associated with the pedal or hand control.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.2.4 Trailer Air-lines (printed 6-5); physical PDF page 89. ↗
After coupling a spring-braked trailer, you discover that its service and supply air lines were crossed. What problem can this cause?
Correct answer: The trailer reservoirs may not charge, so the spring brakes may not release.
Crossed lines may send supply air into the service line instead of charging the reservoirs and releasing spring brakes. Verify correct connections and test trailer braking before driving.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.2.5 Hose Couplers - Crossed Lines (printed 6-6); physical PDF page 90. ↗
Before backing the tractor under a semitrailer, how should its front height relate to the fifth wheel?
Correct answer: Low enough that the tractor raises the trailer slightly as it backs under.
Correct height supports proper engagement. A trailer set too high can miss the locking mechanism; one set too low can be damaged.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.4.1 Step 6 - Check Trailer Height (printed 6-8); physical PDF page 92. ↗
A gentle coupling pull-test seems satisfactory. During the visual check, the jaws appear around the kingpin head instead of its shank. May you depart?
Correct answer: No; the coupling is not correct and must be fixed before travel.
Verify that the jaws close around the kingpin shank, the fifth-wheel plates meet, and the locks are secured. A tug alone does not replace the visual check.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.4.1 Step 13 - Inspect Coupling (printed 6-8 through 6-9; physical PDF 92-93); physical PDF page 92. ↗
A coupled trailer’s landing feet are a few inches above the ground. What remains necessary before departure?
Correct answer: Raise the landing gear fully and secure its crank handle.
Partly raised landing gear can catch on tracks or other obstructions. Fully raise it, secure the handle, and check tractor-to-trailer clearance.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.4.1 Step 15 - Raise Front Trailer Supports (printed 6-9); physical PDF page 93. ↗
While uncoupling, why do you pause with the tractor frame still beneath the trailer after the fifth wheel has cleared?
Correct answer: To check that the landing gear and ground support the trailer, with the frame still available as protection if it drops.
The partial pull-out lets you confirm support before fully clearing the trailer. Firm ground, straight alignment, and correct landing-gear placement are essential.
Source: Maine CDL Manual, currently linked Modernized Testing System manual, operational chapter footers July 2017, 6.4.2 Step 7 - Pull Tractor Partially Clear (printed 6-9); Step 9, physical PDF 94; physical PDF page 93. ↗
