Examkin

Question

Difficulty: Very hardMountain Driving and Steep Downgrades

Proper technique is critical to prevent thermal brake fade when taking a heavy combination vehicle down a steep mountain pass. According to the FMCSA CDL manual, arrange the following actions in the precise chronological sequence required to prepare for the descent and execute the first cycle of proper braking.

  1. 1Determine the safe speed by assessing total vehicle weight, grade profile, and weather conditions.
  2. 2Downshift into a gear no higher than what would be required to climb the same grade, before beginning the descent.
  3. 3Wait until the vehicle accelerates to the established safe speed while relying primarily on engine compression.
  4. 4Depress the service brake pedal firmly enough to feel a definite, steady slowdown.
  5. 5Release the service brakes completely once the speed drops to exactly 5 mph below the safe speed.

Answer

The correct sequence is: Determine safe speed, Downshift before cresting, Wait for vehicle to reach safe speed, Apply brakes firmly, Release brakes at 5 mph below safe speed.
The FMCSA CDL manual mandates a specific, non-negotiable sequence for mountain descents: establishing a safe speed based on conditions, being in the proper low gear before cresting the hill, letting engine braking control the vehicle until the predetermined safe speed is reached, and then executing intermittent snub braking (applying brakes firmly, then releasing them completely when speed drops 5 mph below the safe speed) to manage the thermal load on the braking system.

Step-by-Step Solution

1
Identify the preliminary planning phase of downgrade driving.
Determining the safe speed is established as the first logical step, dictating the parameters for the rest of the descent.
Without a target safe speed, subsequent braking and gearing decisions cannot be made accurately.
2
Determine the precise timing for transmission gear selection.
Downshifting is placed as the second step, which must occur before starting down the grade.
The FMCSA strictly warns against attempting to downshift while descending, as the driver may get caught in neutral with no engine braking.
3
Identify the vehicle's initial behavior upon starting the descent.
The driver allows the vehicle to descend under engine braking until gravity accelerates it to the safe speed limit.
Service brakes must be saved for when they are actually needed, maximizing cooling time.
4
Determine the proper method to apply the service brakes.
Brakes are applied firmly to feel a definite slowdown once the safe speed is reached.
This initiates the snub braking technique, which prevents the excessive heat buildup associated with continuous light pedal pressure.
5
Establish the exact criterion for releasing the service brakes.
Brakes are completely released when the speedometer reads 5 mph below the safe speed.
This completes the first snub braking cycle, providing the necessary interval for the brake drums to cool as the vehicle slowly accelerates back to the safe speed.

Key Concept

Mountain Driving Preparation and Snub Braking Sequence
Rate this question

Topics

Mountain Driving and Steep Downgrades

More questions from this topic