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Difficulty: HardSpeed on Curves and Downgrades

A commercial vehicle operator is descending a sustained 5% downgrade with a safe speed established at 35 mph. Halfway down the grade, the driver encounters a warning sign for an impending sharp bend with an advisory speed of 25 mph. What is the most appropriate speed and braking management technique for the driver to negotiate this section safely without causing brake fade or vehicle instability?

  1. A
    Maintain the 35 mph downgrade speed until reaching the curve entrance, then apply firm, steady service brake pressure while actively steering through the radius to reach 25 mph.
  2. Downshift to a lower gear and use snub braking to bring the vehicle speed below the advisory limit prior to entering the bend, then maintain gentle acceleration through the curve.Answer
  3. C
    Apply continuous, light pedal pressure against the service brakes to gradually bleed speed from 35 mph down to 25 mph across the entire descent and through the turn.
  4. D
    Engage the engine retarder at its maximum setting on wet pavement while downshifting mid-turn to rapidly decrease momentum without using the service brakes.

Answer

Downshift to a lower gear and use snub braking to bring the vehicle speed below the advisory limit prior to entering the bend, then maintain gentle acceleration through the curve.
The correct answer emphasizes completing all required deceleration before the vehicle enters the curve. By selecting a gear low enough to hold the lower speed and using intermittent snub braking to drop the speed below the advisory limit prior to the turn, the driver avoids brake fade and preserves full lateral traction for steering.

Step-by-Step Solution

1
Evaluate the changing operating conditions from a straight downgrade descent to a sharp curve.
Identified that the established safe speed must decrease from 35 mph to below the 25 mph advisory speed before the vehicle enters the curve.
Centrifugal force and rollover risks are significantly magnified in heavy commercial vehicles if entered above a safe speed.
2
Select the appropriate gear and apply the snub braking method prior to curve entry.
Vehicle slows to approximately 20 mph in a proper lower gear before entering the turn.
All speed reduction must take place in a straight line before entering the turn to prevent wheel lockup and brake overheating.
3
Steer through the curve with a light pull of engine power.
Drive wheels maintain traction and stability throughout the radius.
Gentle throttle stabilizes vehicle suspension and keeps drive tires gripping the road surface.

Key Concept

Speed Management on Curves and Downgrades
Estimated Time:1m 30s
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Topics

Speed on Curves and Downgrades

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