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Difficulty: HardSpeed and Road Conditions

A commercial motor vehicle is traveling at 60 mph on a highway when a sudden downpour creates standing water on the roadway. Ahead, the driver approaches a shaded highway overpass that leads into a sharp curve. Which sequence of actions must the driver take to maintain vehicle control and minimize the risk of skidding or hydroplaning?

  1. Reduce speed to approximately 40 mph before entering the curve, turn off the engine retarder, and steer smoothly without braking inside the curve.Answer
  2. B
    Maintain 60 mph until entering the curve, then apply firm service braking while turning and keep the engine retarder fully engaged to maximize deceleration.
  3. C
    Reduce speed to 40 mph while keeping the engine retarder set to maximum to reduce thermal wear on the foundation brakes across the wet bridge deck.
  4. D
    Maintain the posted 60 mph limit but increase following distance, relying on the vehicle's anti-lock braking system (ABS) to compensate for reduced pavement friction.

Answer

Reduce speed to approximately 40 mph before entering the curve, turn off the engine retarder, and steer smoothly without braking inside the curve.
Safe commercial vehicle operation in wet conditions with upcoming curves requires three critical adjustments: reducing speed by approximately one-third (from 60 mph to 40 mph), disabling the engine retarder to prevent drive-axle wheel slippage, and completing all deceleration before entering the curve.

Step-by-Step Solution

1
Calculate the required wet road speed reduction from 60 mph.
Reduce speed by one-third (60 mph minus 20 mph = 40 mph).
Commercial driver regulations require reducing speed by about 1/3 on wet pavement to account for increased stopping distance and hydroplaning risks.
2
Disable auxiliary braking mechanisms including engine retarders.
Retarder is turned off before encountering standing water and shaded overpasses.
Retarders apply braking force only to the drive axles, which can cause wheel lockup and immediate skidding on wet or slippery surfaces.
3
Adjust vehicle speed prior to entering the curve rather than during the turn.
Vehicle enters the curve at the safe target speed of 40 mph or lower under smooth steering control.
Braking within a curve overtaxes lateral tire adhesion and can initiate an unrecoverable jackknife or spinout.

Key Concept

Speed adjustment, retarder safety, and curve management under wet and slippery road conditions
Estimated Time:1m 30s
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Topics

Speed and Road Conditions

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