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Question

Difficulty: EasySpeed on Curves and Downgrades

When negotiating a roadway curve, why must a commercial motor vehicle driver reduce their speed before entering the curve rather than braking while turning?

  1. A
    Tires gain additional lateral traction when firm service braking is applied throughout the turn.
  2. Braking inside the curve can cause the wheels to lock up and lead to a dangerous skid.Answer
  3. C
    Engine retarders automatically disengage when braking is delayed until the middle of the curve.
  4. D
    Driver perception and reaction distance is completely eliminated once the vehicle is actively turning.

Answer

Braking inside the curve can cause the wheels to lock up and lead to a dangerous skid.
Adjusting speed to a safe level before entering a curve is essential because applying brakes while turning transfers vehicle weight and demands simultaneous cornering and stopping traction. If brakes are applied heavily in a turn, the wheels can easily lock up, resulting in a loss of directional control and a serious skid or rollover.

Step-by-Step Solution

1
Identify the primary vehicle dynamics at work when turning along a curved path.
Tires must share available friction between lateral (steering) forces and longitudinal (braking/accelerating) forces.
Applying brakes while turning demands more total traction than the road-tire contact patch may provide.
2
Determine the required safety procedure for curve entry.
The vehicle must be slowed to a safe speed in a straight line before entering the curve.
Slowing down in advance eliminates the need to apply brakes inside the turn, keeping tires within traction limits.

Key Concept

Speed adjustment before entering curves
Estimated Time:45s
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Topics

Speed on Curves and Downgrades

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