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Difficulty: MediumSpeed on Curves and Downgrades

A commercial driver is operating a loaded vehicle along an unfamiliar winding highway with rolling hills and steep descents. Which procedure should the driver follow to maintain directional control and prevent brake failure when managing speed on curves and downgrades?

  1. A
    Downshift into a lower gear after starting down the grade, then apply continuous light pedal pressure to counteract gravitational acceleration.
  2. Reduce vehicle speed before entering each curve, downshift to a safe gear before starting down a grade, and utilize intermittent snub braking to control descent speed.Answer
  3. C
    Maintain normal travel speed until entering the curve, then apply firm brake pressure while steering to settle the vehicle's suspension.
  4. D
    Engage maximum engine retarder braking while steering through sharp wet curves to eliminate the need for service foundation brakes.

Answer

Reduce vehicle speed before entering each curve, downshift to a safe gear before starting down a grade, and utilize intermittent snub braking to control descent speed.
The correct procedure requires decelerating in a straight line before entering curves, engaging a low gear prior to cresting the grade, and using snub braking on the descent. This preserves steering traction and prevents thermal brake fade.

Step-by-Step Solution

1
Analyze tire traction and steering physics on curves.
Identify that speed must be reduced before curve entry to preserve full tire adhesion for directional steering.
Braking inside the curve forces tires to share traction between turning and braking forces, precipitating skids or rollovers.
2
Determine proper gear selection procedure for descending grades.
Establish that downshifting must be completed before the vehicle begins the downhill descent.
Attempting to shift gears on a downgrade can result in missing the gear and becoming stranded in neutral.
3
Evaluate foundation brake cooling and thermal management during prolonged descent.
Apply intermittent snub braking by applying firm pressure until speed drops 5 mph5\text{ mph} below the safe speed, then releasing.
Continuous light pedal pressure causes brake linings to overheat and expand drums, resulting in thermal brake fade.

Key Concept

Safe commercial vehicle operation on curves and downgrades mandates pre-entry deceleration, selecting a low transmission gear before descent, and employing snub braking to avoid brake fade.
Estimated Time:1m 0s
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Topics

Speed on Curves and Downgrades

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