A combination vehicle with a gross weight of 76{}000\text{ lbs} is traveling down a 5\% pa… — Commercial Driver's License (CDL) General Knowledge Exam

A combination vehicle with a gross weight of $76{}000\text{ lbs}$ is traveling down a $5\%$ paved downgrade. The transmission is in the appropriate low gear, and the driver identifies $35\text{ mph}$ as the safe maximum speed for the hill. As the vehicle accelerates to $35\text{ mph}$ , which action should the driver take to control speed effectively and prevent brake fade?

A
Apply steady, gentle pressure on the foot pedal without releasing to hold the vehicle precisely at $35\text{ mph}$ .
Apply the service brakes firmly to slow the vehicle to $30\text{ mph}$ , then release the pedal completely until speed returns to $35\text{ mph}$ .Answer
C
Shift the transmission into neutral to disengage the drivetrain and pump the foot brake repeatedly between $25\text{ mph}$ and $35\text{ mph}$ .
D
Activate maximum retarder power while intermittently tapping the trailer hand valve to lock the trailer wheels.

Answer

Apply the service brakes firmly to slow the vehicle to

30\text{ mph}

, then release the pedal completely until speed returns to

35\text{ mph}

The proper snub braking technique requires applying the brakes hard enough to feel a definite slowdown until speed is reduced to

5\text{ mph}

below the safe speed (from

35\text{ mph}

down to

30\text{ mph}

). Once reduced, the driver releases the brakes completely, allowing the foundation brakes to cool while engine compression holds speed until it climbs back to

35\text{ mph}

, at which point the cycle is repeated.

Step-by-Step Solution

Determine and establish the safe maximum speed based on vehicle weight and grade.

Safe speed established at

35\text{ mph}

in a low gear.

Engine braking in the proper low gear serves as the primary speed-retardation mechanism on downgrades.

Monitor speed until it reaches the safe maximum speed of

35\text{ mph}

, then apply the service brakes firmly.

Vehicle slows down by

5\text{ mph}

30\text{ mph}

within roughly 3 seconds.

Firm application provides noticeable deceleration without dragging the linings continuously.

Release the brake pedal completely once road speed drops to

30\text{ mph}

Vehicle momentum gradually builds back up toward

35\text{ mph}

Releasing the pedal allows the brake drums and linings to dissipate heat into the surrounding air, preventing brake fade.

Key Concept

Proper Snub Braking Technique on Steep Downgrades

Estimated Time:1m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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