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: CA Commercial Driver Handbook § 6.1.1 Rollover Risks ↗
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: CA Commercial Driver Handbook § 6.1.2 Steer Gently ↗
Why can an empty combination vehicle be harder to stop smoothly than a fully loaded one?
Correct answer: Stiff suspension and strong brakes can reduce traction and lock wheels
Light loads can provide poor traction, making wheel lock, trailer swing, and jackknife more likely.
Source: CA Commercial Driver Handbook § 6.1.3 Brake Early ↗
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: CA Commercial Driver Handbook § 6.1.4 Railroad-Highway Crossings ↗
What is the earliest reliable sign that a trailer has started to skid?
Correct answer: The trailer begins moving out of line in the mirrors
Frequent mirror checks during hard braking reveal trailer swing before a jackknife develops.
Source: CA Commercial Driver Handbook § 6.1.5 Prevent Trailer Skids ↗
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: CA Commercial Driver Handbook § 6.1.5 Prevent Trailer Skids ↗
What does off-tracking mean in a turn?
Correct answer: Rear wheels follow a different, tighter path than front wheels
Long vehicles’ rear wheels cut inside the path of their front wheels, with the last trailer cutting in most.
Source: CA Commercial Driver Handbook § 6.1.6 Turn Wide ↗
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: CA Commercial Driver Handbook § 6.1.7 Backing With a Trailer ↗
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: CA Commercial Driver Handbook § 6.2.1 Trailer Hand Valve ↗
What is the tractor protection valve designed to do?
Correct answer: Keep air in the tractor if the trailer breaks away or develops a major leak
The valve closes to protect the tractor air supply when trailer-side pressure is lost.
Source: CA Commercial Driver Handbook § 6.2.2 Tractor Protection Valve ↗
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: CA Commercial Driver Handbook § 6.2.3 Trailer Air Supply Control ↗
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: CA Commercial Driver Handbook § 6.2.4 Trailer Air Lines ↗
What happens when pressure is lost from the trailer emergency line?
Correct answer: Trailer emergency brakes apply and the tractor protection valve closes
Loss of supply-line pressure triggers trailer emergency braking and protects the tractor air supply.
Source: CA Commercial Driver Handbook § 6.2.4 Trailer Air Lines ↗
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: CA Commercial Driver Handbook § 6.2.4 Trailer Air Lines ↗
What danger can result from crossing the trailer service and emergency air lines?
Correct answer: The trailer tanks may not charge and trailer brakes may not work
Crossed connections may prevent spring-brake release or, on older trailers, allow movement without trailer brakes.
Source: CA Commercial Driver Handbook § 6.2.5 Hose Couplers (Glad Hands) ↗
How should trailer air-line shut-off valves be positioned in a multi-trailer combination?
Correct answer: Open except at the rear of the last trailer, where they are closed
Air must flow through every unit, while the unused line ends on the last trailer remain closed.
Source: CA Commercial Driver Handbook § 6.2.7 Shut-off Valves ↗
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: CA Commercial Driver Handbook § 6.2.8 Trailer Service, Parking, and Emergency Brakes ↗
Where is a trailer’s yellow ABS malfunction lamp normally located?
Correct answer: On the left side near a front or rear corner
Trailers equipped with ABS normally display the yellow fault lamp on the left side.
Source: CA Commercial Driver Handbook § 6.3.1 Trailers Required to Have ABS ↗
Why must the fifth-wheel plate be properly lubricated before coupling?
Correct answer: Excess friction can create steering problems
The tractor and trailer must articulate freely across the fifth-wheel surface.
Source: CA Commercial Driver Handbook § 6.4.1 Coupling: Inspect Fifth-Wheel ↗
How should the trailer height be set before backing fully under it?
Correct answer: Low enough to be raised slightly by the tractor
A slightly low trailer contacts the fifth-wheel correctly; excessive height can cause a false coupling.
Source: CA Commercial Driver Handbook § 6.4.1 Coupling: Check Trailer Height ↗
How is the tractor-trailer connection initially tested after the kingpin locks?
Correct answer: Raise the landing gear slightly and pull gently against locked trailer brakes
A gentle pull against the locked trailer brakes is an initial coupling check, not complete proof. Secure the vehicle and also visually check that the fifth-wheel plates meet and the jaws are locked around the kingpin shank before driving.
Source: CA Commercial Driver Handbook § 6.4.1 Coupling: Test for Coupling ↗
Where should the fifth-wheel locking jaws be after proper coupling?
Correct answer: Around the shank of the kingpin
A visual inspection must confirm the jaws fully encircle the kingpin shank with no gap between fifth-wheel plates.
Source: CA Commercial Driver Handbook § 6.4.1 Coupling: Inspect Coupling ↗
Before driving a coupled tractor-semitrailer, how far should the landing gear be raised?
Correct answer: Fully raised with the crank secured
Partly raised gear can strike tracks or road objects and must be fully stowed.
Source: CA Commercial Driver Handbook § 6.4.1 Coupling: Raise Front Trailer Supports ↗
Why should the tractor remain partly under the trailer during the first pull-forward step?
Correct answer: It can support the trailer if the landing gear collapses or sinks
Keeping the tractor frame under the trailer provides temporary support while the landing gear is checked.
Source: CA Commercial Driver Handbook § 6.4.2 Uncoupling: Pull Tractor Partially Clear ↗
How are trailer service brakes checked before normal operation?
Correct answer: Move slowly and apply the trailer hand valve to feel the brakes engage
At low speed, a hand-valve application verifies trailer service brakes; the foot pedal controls them during driving.
Source: CA Commercial Driver Handbook § 6.5.2 Test the Trailer Service Brakes ↗
You find dirt on a glad-hand coupling and its rubber seal before connecting a trailer. What should you do?
Correct answer: Clean the coupler and seal before making the connection
Clean couplers and seals before connecting them. The rubber seal prevents air from escaping, and keeping contamination out protects the air system.
Source: CA Commercial Driver Handbook § 6.2.5 Hose Couplers (Glad Hands) ↗
After disconnecting a trailer, where should the tractor’s air-line couplers be attached if dummy couplers are provided?
Correct answer: To the dummy couplers to keep dirt and water out
Dummy or dead-end couplers protect unused air lines from water and dirt. Use them when the hoses are not connected to a trailer.
Source: CA Commercial Driver Handbook § 6.2.5 Hose Couplers (Glad Hands) — Dummy Couplers ↗
When you press the foot brake, what determines how much pressure the relay valves send from the trailer reservoirs to its brakes?
Correct answer: The pressure in the service line
Service-line pressure communicates the braking demand to the relay valves. The trailer’s own reservoirs supply the air sent to its brakes.
Source: CA Commercial Driver Handbook § 6.2.6 Trailer Air Tanks ↗
A major trailer service-line leak may become obvious only when you apply the brakes. What can happen then?
Correct answer: Air pressure can fall rapidly and eventually apply the trailer emergency brakes
A service-line leak may not be apparent until braking pressurizes that line. The resulting air loss can rapidly lower tank pressure; at sufficiently low pressure, trailer emergency brakes can apply.
Source: CA Commercial Driver Handbook § 6.2.8 Trailer Service, Parking, and Emergency Brakes ↗
A tractor-trailer has ABS on the trailer but not on the tractor. Which statement is correct?
Correct answer: Trailer ABS still helps, but the tractor can still lose control under braking
ABS on the trailer alone can reduce trailer swing, but it does not prevent tractor wheel lock or every jackknife. Monitor both units and use only the braking force needed to stop safely and retain control.
Source: CA Commercial Driver Handbook § 6.3.2 Braking With ABS ↗
Does an automatic drain eliminate the handbook’s advice to check trailer air tanks for accumulated moisture?
Correct answer: No; open the drains to check, because automatic drains remove most moisture, not necessarily all of it
The handbook says to drain each trailer air tank daily and still open drains to check tanks with automatic drains. Water and oil accumulation can interfere with correct brake operation.
Source: CA Commercial Driver Handbook § 6.2.6 Trailer Air Tanks ↗
Before backing a tractor under a trailer, what must prevent the trailer from rolling?
Correct answer: Applied spring brakes or appropriate wheel chocks
Coupling forces can move an unsecured trailer. Check the area and its securement first.
Source: CA Commercial Driver Handbook § 6.4.1 Step 2 — Area and Wheels ↗
Why should the tractor be straight in front of the trailer before coupling?
Correct answer: An angled approach can push the trailer sideways and damage its landing gear
Align the units rather than use the tractor to force the trailer sideways.
Source: CA Commercial Driver Handbook § 6.4.1 Step 3 — Position the Tractor ↗
How should air lines be arranged before you finish backing under the trailer?
Correct answer: Supported clear of places where they could be crushed or caught
Line support must protect the connections during coupling and later movement.
Source: CA Commercial Driver Handbook § 6.4.1 Step 7 — Connect Air Lines ↗
What reverse gear and speed are appropriate for the final coupling movement?
Correct answer: Lowest reverse gear at a slow, controlled speed
Avoid striking the kingpin hard while completing the connection.
Source: CA Commercial Driver Handbook § 6.4.1 Step 10 — Back Under the Trailer ↗
Before going underneath to inspect the coupling, how should you secure the tractor?
Correct answer: Parking brakes on, transmission neutral, engine off, and key with you
Prevent someone moving the rig while you inspect underneath.
Source: CA Commercial Driver Handbook § 6.4.1 Step 12 — Secure the Vehicle ↗
You see a gap between the trailer’s upper plate and the fifth-wheel plate after coupling. What should you do?
Correct answer: Do not drive until the coupling problem is corrected
A gap can mean the kingpin is resting above the jaws rather than being correctly locked.
Source: CA Commercial Driver Handbook § 6.4.1 Step 13 — Inspect the Coupling ↗
Besides checking the jaws around the kingpin, which locking parts need inspection?
Correct answer: The locking lever and its safety latch
Verify the complete locking mechanism rather than relying on a tug test alone.
Source: CA Commercial Driver Handbook § 6.4.1 Step 13 — Locking Lever and Safety Latch ↗
Once the trailer’s weight rests on the tractor, which clearances must you check?
Correct answer: Tractor frame to landing gear and tractor tires to trailer nose
Turning or suspension movement must not cause contact between the units.
Source: CA Commercial Driver Handbook § 6.4.1 Step 15 — Clearances ↗
Before uncoupling a loaded trailer, what must you know about the parking surface?
Correct answer: It can support the trailer and landing gear
Landing gear can sink or collapse on an unsuitable surface.
Source: CA Commercial Driver Handbook § 6.4.2 Step 1 — Position the Rig ↗
You are unsure whether the parked trailer has spring brakes. What should you do before uncoupling?
Correct answer: Chock its wheels
Stored air can leak away; use chocks when spring-brake protection is uncertain.
Source: CA Commercial Driver Handbook § 6.4.2 Step 3 — Chock the Trailer Wheels ↗
When uncoupling a loaded trailer, how far should you lower the landing gear after firm ground contact?
Correct answer: A few extra turns in low gear to unload some tractor weight, without lifting off the fifth-wheel
Support some weight to ease release without creating an unsafe gap or over-lifting.
Source: CA Commercial Driver Handbook § 6.4.2 Step 4 — Lower the Landing Gear ↗
How should the disconnected trailer electrical cable be stored?
Correct answer: Supported with the plug pointing down to keep moisture out
Protect the plug from moisture and the cable from moving parts or road damage.
Source: CA Commercial Driver Handbook § 6.4.2 Step 5 — Disconnect Lines and Cable ↗
While operating the fifth-wheel release, where should your legs and feet be?
Correct answer: Clear of the tractor’s rear wheels
Unexpected vehicle movement can cause severe injury near the wheels.
Source: CA Commercial Driver Handbook § 6.4.2 Step 6 — Unlock the Fifth-Wheel ↗
You have pulled the fifth-wheel clear but kept the tractor frame under the trailer. What should you verify before pulling away fully?
Correct answer: The landing gear is sound and the ground supports the trailer
Check support while the tractor is still positioned to limit a trailer fall.
Source: CA Commercial Driver Handbook § 6.4.2 Step 9 — Inspect Trailer Supports ↗
