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Difficulty: HardStopping and Braking Procedures

During a descent on a steep mountain grade where the maximum safe speed is determined to be 35 mph, a driver must employ the proper braking technique to prevent brake fade and maintain vehicle control. Which procedure correctly implements the snub braking technique under these operating conditions?

  1. A
    Maintain continuous, light pedal pressure throughout the downgrade to hold the vehicle steadily at exactly 35 mph without releasing.
  2. B
    Activate maximum auxiliary retarder braking while rapidly pumping the foot brake pedal every few seconds regardless of vehicle speed.
  3. Apply the brakes firmly to feel a definite slowdown until speed reaches 30 mph, then release the brakes fully until speed climbs back to 35 mph before repeating the process.Answer
  4. D
    Allow vehicle speed to reach 45 mph before applying heavy emergency braking down to 20 mph to minimize the overall number of brake applications.

Answer

Apply the service brakes with enough firm pressure to feel a definite slowdown until the vehicle reaches 30 mph (5 mph below safe speed), then release them completely until the vehicle accelerates back to 35 mph before repeating the cycle.
The established commercial driving standard for steep downgrade speed control is snub braking. When the vehicle reaches its safe speed, the driver applies the service brakes firmly to reduce speed to 5 mph below that safe speed over about three seconds, then releases the brakes entirely. This cycle balances effective speed management with crucial cooling phases that prevent brake fade.

Step-by-Step Solution

1
Establish the vehicle in the correct low transmission gear and allow speed to build to the determined safe speed of 35 mph.
Engine braking provides the primary retarding force to control vehicle acceleration down the grade.
Service brakes should only supplement engine braking on downgrades, not act as the sole speed control mechanism.
2
Apply the service brakes firmly for approximately three seconds until the road speed drops to 30 mph (5 mph below the safe speed).
The vehicle slows down in a controlled, predictable manner without causing excessive sustained heat buildup.
Firm, brief braking provides effective deceleration while minimizing the total time friction surfaces are generating heat.
3
Release the brake pedal completely and keep it released until gravity accelerates the vehicle back to the safe speed of 35 mph.
Brake linings and drums cool down as air flows around the wheels during the unbraked interval.
Complete release allows heat dissipation, preventing drum expansion and thermal brake fade.

Key Concept

Snub Braking Technique and Thermal Management
Estimated Time:1m 30s
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Topics

Stopping and Braking Procedures

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