Which combination best reduces rollover risk in a combination vehicle?
Correct answer: Keep cargo low and slow down for turns
A low, centered load and reduced turn speed keep the center of gravity controlled.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.1 Rollover Risks, printed page 6-1 (physical PDF page 89) ↗
What can the crack-the-whip effect do during a sudden lane change?
Correct answer: Cause the rear trailer to overturn
Rearward amplification makes steering movement more severe toward the back of a multi-unit combination.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.2 Steer Gently, printed page 6-1 (physical PDF page 89) ↗
Why can an empty combination vehicle be harder to stop smoothly than a fully loaded one?
Correct answer: Light loading can cause wheel lock and poor traction
Light loads can provide poor traction, making wheel lock, trailer swing, and jackknife more likely.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.3 Brake Early, printed page 6-1 (physical PDF page 89) ↗
What should a driver do first if a low-clearance combination becomes stuck on railroad tracks?
Correct answer: Leave the vehicle and move away from the tracks
Occupants should get away from the tracks, then use the crossing information to contact emergency services.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.4 Railroad-highway Crossings, printed page 6-2 (physical PDF page 90) ↗
What is the earliest reliable sign that a trailer has started to skid?
Correct answer: Trailer misalignment appears in the mirrors
Frequent mirror checks during hard braking reveal trailer swing before a jackknife develops.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.5 Prevent Trailer Skids, Recognize the Skid, printed page 6-2 (physical PDF page 90) ↗
How should a driver respond when trailer wheels lock and the trailer starts to swing?
Correct answer: Release the brakes to restore traction
The locked trailer brakes caused the skid; releasing them lets the tires regain grip.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.5 Stop Using the Brake, printed page 6-3 (physical PDF page 91) ↗
What does off-tracking mean in a turn?
Correct answer: Rear wheels cut inside the front-wheel path
Long vehicles’ rear wheels cut inside the path of their front wheels, with the last trailer cutting in most.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.6 Turn Wide, printed page 6-3 (physical PDF page 91) ↗
When backing a trailer on a curved path, which side is preferred?
Correct answer: The driver’s side
Driver-side backing provides the clearest view; straight-line backing is preferable whenever possible.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.1.7 Backing with a Trailer, printed page 6-3 (physical PDF page 91) ↗
What is the proper routine use of a trailer hand valve?
Correct answer: Testing the trailer brakes
The hand valve is for testing trailer brakes; normal braking should use the foot pedal.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.1 Trailer Hand Valve, printed page 6-4 (physical PDF page 92) ↗
What is the tractor protection valve designed to do?
Correct answer: Preserve tractor air after a major trailer leak
The valve closes to protect the tractor air supply when trailer-side pressure is lost.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.2 Tractor Protection Valve, printed page 6-5 (physical PDF page 93) ↗
On a newer tractor, what does pulling out the red eight-sided trailer-air-supply knob do?
Correct answer: Shuts off trailer air and applies trailer emergency brakes
Pulling the red knob closes the supply; pushing it in supplies air to the trailer.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.3 Trailer Air Supply Control, printed page 6-5 (physical PDF page 93) ↗
What are the two air lines on a combination vehicle?
Correct answer: Service and emergency
The service line carries brake-control pressure, while the emergency line supplies tanks and controls emergency braking.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.4 Trailer Air-lines, printed page 6-5 (physical PDF page 93) ↗
What happens when pressure is lost from the trailer emergency line?
Correct answer: Trailer emergency braking and tractor protection activate
Loss of supply-line pressure triggers trailer emergency braking and protects the tractor air supply.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.4 Emergency Air-line, printed page 6-5 (physical PDF page 93) ↗
Which color normally identifies the trailer emergency air line?
Correct answer: Red
Emergency or supply lines are normally red; service lines are normally blue.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.4 Trailer Air-lines / 6.2.5 Hose Couplers, printed page 6-5 (physical PDF page 93) ↗
What danger can result from crossing the trailer service and emergency air lines?
Correct answer: Tanks may not charge; brakes may fail
Crossed connections may prevent spring-brake release or, on older trailers, allow movement without trailer brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.5 Hose Couplers, crossed lines (continued), printed page 6-6 (physical PDF page 94) ↗
How should trailer air-line shut-off valves be positioned in a multi-trailer combination?
Correct answer: Open through the rig; closed at the final rear
Air must flow through every unit, while the unused line ends on the last trailer remain closed.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.7 Shut-off Valves, printed page 6-6 (physical PDF page 94) ↗
Why must wheel chocks be used when parking an older trailer without spring brakes?
Correct answer: Stored air can leak away and release its emergency brakes
Air-operated emergency brakes on such trailers hold only while stored pressure remains.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.2.8 Trailer Service, Parking and Emergency Brakes, printed page 6-6 (physical PDF page 94) ↗
Where is a trailer’s yellow ABS malfunction lamp normally located?
Correct answer: Left-side front or rear corner
A trailer ABS malfunction lamp is yellow and located on the left side near a front or rear corner. Do not confuse it with the red trailer-air-supply control in the tractor cab.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.3.1 Trailers Required to Have ABS, printed page 6-7 (physical PDF page 95) ↗
Why must a fifth-wheel plate that requires grease be properly lubricated before coupling?
Correct answer: Excess friction can create steering problems
Where lubrication is required, excess friction between the tractor and trailer can cause steering problems. Learn the coupling details and maintenance requirements for the equipment you operate.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.4.1 Step 1 Inspect Fifth Wheel, printed page 6-7 (physical PDF page 95) ↗
How should the trailer height be set before backing fully under it?
Correct answer: Low enough to be raised slightly by the tractor
Set the trailer so the tractor raises it slightly while backing under. Too high can prevent proper coupling; too low can damage the trailer nose. Check kingpin and fifth-wheel alignment.
Source: Florida Commercial Driver's License Manual, July 2022, section 6.4.1 Step 6 Check Trailer Height, printed page 6-8 (physical PDF page 96) ↗
