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Difficulty: HardSpeed on Curves and Downgrades

A commercial motor vehicle is operating along a winding highway where rolling downgrades transition directly into unbanked curves. To maintain optimal tire traction and prevent dangerous heat buildup in the foundation brakes, what is the proper procedure for managing speed through these sections?

  1. A
    Maintain descent speed along the straightaways and apply firm service braking mid-curve once lateral force is detected.
  2. Shift into a proper low gear before the descent, reduce speed on straight sections prior to entering each curve, and rely primarily on engine braking.Answer
  3. C
    Keep continuous, light pedal pressure on the service brakes throughout the entire downhill and turn sequence to hold an exact speed.
  4. D
    Coast in neutral on straight downhill segments to cool the drivetrain, applying maximum service braking just as the vehicle reaches the curve apex.

Answer

Shift into a proper low gear before the descent, reduce speed on straight sections prior to entering each curve, and rely primarily on engine braking.
Selecting a low gear before beginning the descent enables engine compression to hold vehicle speed check, while completing speed reduction on straight sections before curve entry ensures all available tire traction is dedicated to steering control rather than braking.

Step-by-Step Solution

1
Select the proper transmission gear prior to starting down the grade.
The vehicle utilizes engine compression braking as the primary speed-retarding force.
Engine braking limits the need for continuous service brake applications, keeping brake components cool.
2
Complete all necessary service brake deceleration on straight stretches before turning.
The vehicle enters the curve at or below safe advisory speed without requiring brake application during steering.
Tires have a finite traction envelope; dividing traction between heavy braking and cornering causes wheel lockup and skidding.
3
Maintain smooth throttle or steady momentum through the curve and resume proper snub braking cycles on subsequent straight downgrades if needed.
Directional stability is preserved and brake drum temperatures remain within safe limits.
Proper snub braking and smooth cornering prevent thermal fade and lateral weight transfer instability.

Key Concept

Engine braking gear selection combined with pre-curve speed reduction preserves tire traction and prevents thermal brake fade.
Estimated Time:1m 30s
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Topics

Speed on Curves and Downgrades

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