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Difficulty: HardSpeed and Road Conditions

A commercial combination vehicle is traveling at a speed of 54 mph54\text{ mph} on dry pavement when a sudden downpour leaves standing water on the roadway ahead of a sharp highway transition curve. According to official commercial driver safety standards for managing speed and road conditions, which course of action should the driver take to maintain vehicle control?

  1. A
    Maintain cruising speed until reaching the curve, then apply firm service brakes while navigating through the turn to bleed off momentum.
  2. Reduce speed by one-third to 36 mph36\text{ mph} before entering the curve, disengage the engine retarder, and ease off the accelerator without braking if hydroplaning occurs.Answer
  3. C
    Maintain 54 mph54\text{ mph} through the wet surface and set the engine retarder to maximum power to stabilize the drive wheels.
  4. D
    Reduce speed by only 5 mph5\text{ mph}, assuming that total stopping distance is determined strictly by mechanical braking friction without accounting for increased reaction buffer needs.

Answer

Reduce speed by one-third to 36 mph36\text{ mph} before entering the curve, disengage the engine retarder, and ease off the accelerator without braking if hydroplaning occurs.
The correct action requires slowing down by one-third of dry-road cruising speed (reducing 54 mph54\text{ mph} down to 36 mph36\text{ mph}) before reaching the transition curve. In addition, the engine retarder must be switched off because auxiliary driveline braking on wet roads can induce a catastrophic drive-wheel skid. Finally, should standing water cause hydroplaning, the driver must smoothly release the accelerator and refrain from hard braking to allow the tires to regain traction.

Step-by-Step Solution

1
Calculate the mandated wet pavement speed reduction.
On a wet road, a commercial vehicle must reduce speed by approximately one-third (1/31/3). One-third of 54 mph54\text{ mph} is 18 mph18\text{ mph}, so 54 mph−18 mph=36 mph54\text{ mph} - 18\text{ mph} = 36\text{ mph}.
Wet surfaces reduce tire-to-pavement friction and dramatically increase braking distance.
2
Determine proper curve entry timing.
The speed reduction must occur completely prior to entering the curve.
Braking within a curve transfers lateral load and easily exceeds available tire traction, inducing skids or rollovers.
3
Manage auxiliary braking systems and hydroplaning risks.
Turn off engine retarders and release the accelerator smoothly if water causes wheels to lose contact with the road.
Retarders can lock drive wheels on slippery surfaces, and hard braking while hydroplaning causes immediate loss of steering control.

Key Concept

Speed adjustment, retarder management, and hydroplaning response under wet roadway and curve conditions
Estimated Time:1m 30s
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Topics

Speed and Road Conditions

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