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Question

Difficulty: MediumSpeed and Road Conditions

You are operating a commercial motor vehicle on a highway with a posted speed limit of 55 mph when a heavy rain shower begins, leaving standing water across the roadway. According to commercial driving safety standards, which action should you take regarding your speed and vehicle controls?

  1. A
    Maintain the posted speed on straight sections and apply firm braking only after entering standing water or curved sections.
  2. Reduce your vehicle speed by about one-third to approximately 35 to 37 mph and turn off the engine retarder.Answer
  3. C
    Reduce speed by one-third while engaging the engine retarder to maximum strength to assist braking.
  4. D
    Maintain the posted speed limit, relying on heavy cargo weight to maintain tire grip and normal stopping distance.

Answer

Reduce your vehicle speed by about one-third to approximately 35 to 37 mph and turn off the engine retarder.
On wet roadways, commercial drivers must reduce their speed by approximately one-third (from 55 mph to around 35–37 mph) to maintain adequate traction and control stopping distance. Furthermore, engine retarders must always be turned off on wet or slippery surfaces because the mechanical drag applied to the drive wheels can cause them to lose traction and trigger a serious skid.

Step-by-Step Solution

1
Calculate the required wet-road speed reduction.
Reduce speed by about one-third from 55 mph down to approximately 35–37 mph.
Commercial driving standards mandate reducing speed by roughly one-third on wet pavement to manage increased stopping distance and avoid hydroplaning.
2
Determine proper auxiliary brake (retarder) configuration.
Disengage or turn off the engine retarder.
Retarders can cause drive wheels to lock up and break traction when road surfaces are wet, snow-covered, or icy.

Key Concept

Speed reduction and retarder safety on wet pavement
Estimated Time:1m 0s
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Topics

Speed and Road Conditions

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