CDL Combination Vehicles Test

B. Replace the belt immediately before operating the vehicle.

A frayed and cracked air compressor drive belt indicates significant wear and a high risk of failure. A failed belt would lead to a loss of air pressure for the braking system, making the vehicle unsafe to operate. Immediate replacement is necessary.

D. Check blind spots by turning their head to confirm no vehicles are present.

Combination vehicles have large blind spots, especially along their sides. After checking mirrors, a head check is essential to visually confirm that no vehicles are hidden in these areas before starting the lane change.

B. Approach the intersection close to the centerline or left side of the lane, then turn left.

For a left turn in a combination vehicle, approaching close to the centerline allows the vehicle to make a wider sweep, preventing the trailer from cutting the corner and hitting curbs or other vehicles.

B. Slightly reduce speed to increase the following distance for the vehicle ahead, allowing the tailgater more room to pass.

Reducing speed slightly increases the space ahead of your vehicle, which provides a larger cushion if you need to brake suddenly. This also gives the tailgating driver more opportunity to pass safely.

B. Apply the trailer hand brake gently and steadily.

Gently applying the trailer hand brake (trailer brake control) helps to pull the trailer straight by creating drag on the trailer wheels, without affecting the tractor's stability. This can often correct minor sway before it becomes uncontrollable.

A. Apply steady, firm pressure to the brake pedal until the vehicle stops.

With ABS, the most effective emergency braking technique is to apply steady, firm pressure to the brake pedal. The ABS system will automatically modulate brake pressure to prevent wheel lock-up, allowing the driver to maintain steering control.

B. The weight of the vehicle and its cargo.

The weight of the vehicle and its cargo is the most critical factor. Heavier vehicles build up more momentum and require significantly more braking power to control speed on a downgrade, increasing the risk of brake fade. A safe speed is one that allows for controlled braking without overheating the brakes.

D. Disconnect the trailer air lines and lock the trailer coupling (kingpin) with a security device.

Disconnecting air lines renders the trailer brakes inoperable, making it difficult to move. Locking the kingpin prevents another tractor from coupling to and stealing the trailer, making this the most effective security measure.

C. Brake linings are worn to less than 1/4 inch thickness.

Brake linings worn to less than 1/4 inch thickness (or to the wear indicator if present) are considered critically worn and must be replaced immediately to ensure effective braking and prevent metal-to-metal contact.

D. There is an excessive air leak in the brake system.

This scenario describes the air loss rate test. For combination vehicles, with the engine off and foot brake fully applied, an air pressure drop of more than 4 psi in one minute indicates excessive leaks in the air brake system, which is a critical safety defect.

D. The hand valve applies only the trailer service brakes, while the foot brake applies both tractor and trailer service brakes.

The trailer hand valve (trolley valve) is designed to apply only the service brakes on the trailer(s). This is useful for testing or to prevent a jackknife by gently applying trailer brakes. The foot brake pedal, however, applies the service brakes on both the tractor and the trailer(s) simultaneously.

A. The length of your combination vehicle and the available clear sight distance ahead.

The length of a combination vehicle significantly increases the time and distance required to pass. Insufficient clear sight distance ahead is the most critical hazard, as it directly impacts the safety margin for completing the maneuver.

C. The weight of the vehicle and its cargo.

The weight of the vehicle and its cargo (Gross Combination Weight, GCW) is the most critical factor in determining a safe descent speed. Heavier vehicles build up speed faster and require more braking effort, increasing the risk of brake fade on downgrades. The GCWR is the maximum allowed, but the actual GCW determines the current braking demand.

B. Check for leaks in the cooling system immediately.

While topping off coolant is often necessary, a low coolant level discovered during a post-trip inspection, especially if it was normal during the pre-trip, suggests a potential leak. The most appropriate first action is to investigate for leaks before simply adding more coolant.

D. Gently move to the left side of your lane to provide more space for the passing vehicle.

When another vehicle is attempting to pass, especially on the right where visibility might be reduced, it's a defensive driving practice to provide as much space as possible. Gently moving to the left within your lane, if safe, allows more room for the other vehicle to complete its maneuver without increasing risk.

C. Refer to the bill of lading or shipping papers for the cargo weight and add it to the tractor and trailer's empty weight.

The bill of lading provides the accurate cargo weight. Adding this to the known empty weights of the tractor and trailer (which can be found on vehicle registrations or specifications) gives the actual gross vehicle weight, which must be compared to the bridge limit.

A. Replace the glad hand gaskets or the glad hands themselves before driving.

Corroded glad hands or leaking gaskets can lead to a loss of air pressure in the trailer's braking system, which is a critical safety hazard. They must be repaired or replaced before the vehicle is operated.

C. Apply firm, steady pressure to the brake pedal.

With ABS, the correct technique for emergency braking is to apply firm, steady pressure to the brake pedal. The ABS system will automatically modulate brake pressure to prevent wheel lock-up, allowing you to maintain steering control.

A. Every 5-8 seconds, or more often in heavy traffic.

Constant scanning of mirrors (every 5-8 seconds) is a critical defensive driving technique for combination vehicle operators. This frequency ensures you are continuously aware of surrounding traffic, blind spots, and potential hazards, allowing for timely reactions.

D. Anticipate unexpected movements from other vehicles and pedestrians, and use spotters if available for backing.

Truck stops are high-risk areas due to congestion, tight spaces, and varied vehicle and pedestrian movements. Anticipating the unpredictable actions of others and actively using spotters for maneuvers like backing are critical defensive strategies for combination vehicles to prevent accidents.

A. Apply the trailer hand brake gently and smoothly.

Gently and smoothly applying the trailer hand brake (if available and safe to do so) will help to straighten out the trailer by applying braking force directly to the trailer wheels, pulling it back in line with the tractor. This action slows the trailer more than the tractor, which can reduce sway.

B. A blown fuse specifically for the brake light circuit in the tractor or trailer.

If only the brake lights are out while other lights function, it points to an issue specific to the brake light circuit. A blown fuse on that circuit is a common and probable cause, as a general short or ground issue would likely affect more lights.

B. A restriction in the air line to the front brake reservoir.

A significant difference in pressure between the front and rear brake systems in a dual air system, with one system being low, strongly suggests a restriction or leak preventing proper air flow to that specific reservoir or brake circuit.

D. To allow air to flow from the wet tank to the other tanks, but not back.

The one-way check valve prevents air from flowing back into the wet tank from the primary or secondary tanks. This ensures that if the air compressor or wet tank develops a leak, the primary and secondary (service) air tanks retain pressure, allowing for continued braking capability.

A. Vary eye focus, frequently scan mirrors, and observe roadside activity.

Highway hypnosis occurs when a driver stares straight ahead for long periods, leading to a trance-like state. Actively varying eye focus, constantly scanning mirrors, and observing the environment helps keep the brain engaged and prevents this dangerous condition.