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Question

Difficulty: MediumSpeed on Curves and Downgrades

An operator driving a heavy combination vehicle approaches a sharp curve on an unfamiliar roadway. Which procedure should the driver follow to maintain maximum vehicle stability and control throughout the curve?

  1. A
    Enter the curve at cruising speed and apply continuous service brake pressure through the apex to keep the combination unit aligned.
  2. Slow down to a safe speed and downshift to the proper gear before entering the turn, then accelerate slightly while rounding the curve.Answer
  3. C
    Maintain regular highway speed into the turn, then downshift to a lower gear midway through the curve to take advantage of engine braking.
  4. D
    Engage maximum auxiliary retarder braking upon entering the turn to quickly drop speed without heating the wheel service brakes.

Answer

Slow down to a safe speed and downshift to the proper gear before entering the turn, then accelerate slightly while rounding the curve.
Slowing to a safe speed and completing downshifts before entering a curve preserves available tire traction exclusively for steering. Applying light engine power while rounding the turn stabilizes the vehicle chassis and prevents drive-wheel lockup.

Step-by-Step Solution

1
Assess the approach and recognize that vehicle weight and high center of gravity require a substantial speed reduction prior to curve entry.
Driver identifies that slowing must take place on a straight path before the vehicle starts turning.
Tires provide limited traction that must be shared between directional steering forces and braking forces.
2
Apply service brakes smoothly while travelling straight to reach a safe negotiating speed, downshift to the gear needed to pull through the curve, and release the brake pedal.
Vehicle enters the curve in the correct gear at a controlled speed without active brake application.
Completing all deceleration and downshifting before the turn prevents wheel slippage and transmission shock loads while steering.
3
Steer smoothly through the curve while maintaining slight engine throttle.
The combination vehicle tracks steadily and maintains lateral stability through the apex and exit of the turn.
Gentle acceleration helps keep the combination taut and balanced without exceeding the tire adhesion limit.

Key Concept

Pre-curve speed reduction, gear selection, and traction management
Estimated Time:1m 0s
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Topics

Speed on Curves and Downgrades

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