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Question

Difficulty: EasySpeed on Curves and Downgrades

When approaching an off-ramp or sharp roadway curve with a posted advisory speed limit, why might traveling at the posted advisory speed still be unsafe for a commercial motor vehicle?

  1. A
    Commercial vehicles need to accelerate through curves to generate stabilizing outward centrifugal force.
  2. B
    Service brakes must be applied continuously while steering through the turn to compensate for reaction distance.
  3. Posted advisory speeds are generally set for passenger cars and can cause a commercial vehicle with a high center of gravity to roll over.Answer
  4. D
    Drivers must shift into neutral and rely strictly on the engine retarder to control speed inside the curve.

Answer

Posted advisory speeds are generally set for passenger cars and can cause a commercial vehicle with a high center of gravity to roll over.
The correct answer identifies that posted curve advisory speeds are established for passenger vehicles. Because commercial trucks have a significantly higher center of gravity and carry heavy loads, they can roll over at speeds that passenger cars navigate with ease. Drivers must slow down below the posted advisory speed before entering the curve.

Step-by-Step Solution

1
Identify the standard calibration benchmark for roadway curve advisory speeds.
Advisory speeds are calculated based on the handling characteristics and low center of gravity of passenger cars.
Traffic engineering standards establish curve advisory signs based on typical automobile dynamics.
2
Analyze how commercial motor vehicle physical characteristics interact with lateral forces in a curve.
Commercial vehicles carry heavier loads higher off the ground, resulting in a higher center of gravity.
A higher center of gravity significantly lowers the threshold of lateral force required to induce a vehicle rollover.
3
Determine the proper driver action for curve speed management.
Reduce speed below the posted advisory speed before entering the curve.
Slowing down ahead of the curve ensures the vehicle stays well below its rollover and skid thresholds.

Key Concept

Speed reduction before curves and rollover risk due to high center of gravity
Estimated Time:45s
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Topics

Speed on Curves and Downgrades

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