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Difficulty: MediumHydroplaning and Wet Road Traction Loss

Which statement best explains why a paved road surface is exceptionally slippery during the first few minutes of a light rainfall after a prolonged dry period?

  1. Engine oil and grease accumulated on the road surface mix with water to create a slick coating before heavy rain can wash it away.Answer
  2. B
    Cold rainwater causes the pavement temperature to drop rapidly below freezing, forming a thin layer of surface ice.
  3. C
    Standing water immediately lifts tires off the pavement surface regardless of vehicle speed or tire tread condition.
  4. D
    Rainwater causes vehicle tire rubber to chemically react and lose its natural grip against asphalt.

Answer

Engine oil and grease accumulated on the road surface mix with water to create a slick coating before heavy rain can wash it away.
During dry weather, engine oil, grease, and exhaust residue accumulate on pavement surfaces. When rain first starts, water floats these oily deposits to the surface, forming a slick film. Drivers must slow down immediately during the first few minutes of rain, as traction is often worse than during prolonged heavy rainfall that washes these contaminants away.

Step-by-Step Solution

1
Identify the primary cause of reduced traction during early rainfall.
During dry periods, vehicles drop oil, grease, and dirt onto the road surface.
Road contaminants accumulate in the pores and texture of the asphalt during dry weather.
2
Analyze how water interacts with road surface contaminants when rain begins.
Light rainfall mixes with the oil and grease, bringing them to the surface.
Oil is less dense than water and floats on top, creating a thin, highly slippery emulsion.
3
Evaluate how traction changes as rain continues.
Continued heavier rain eventually washes the oil slick off the road, slightly improving traction compared to the initial slick state.
Sustained rainfall flushes contaminants to the shoulders and drainage systems.

Key Concept

Initial Rain Traction Loss and Wet Surface Slippiness
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Topics

Hydroplaning and Wet Road Traction Loss

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