When are road surfaces the most slippery?

The correct choice highlights that road surfaces are the most slippery when it first starts to rain. This is because, during the initial moments of rainfall, water mixes with oils, dirt, and debris that have accumulated on the road surface. This combination creates a slick layer that significantly reduces traction for vehicles.

As rain begins to fall, the water does not immediately wash away the oils and grime; instead, it acts as a lubricant, leading to hazardous driving conditions. Once sufficient rain falls to wash away these contaminants, the road typically becomes less slippery. Understanding this concept is crucial for drivers because it emphasizes the need for increased caution during the onset of rainfall, as road surfaces can be particularly treacherous at that time.

Contextually, while heavy snow can create a slippery environment, and cold temperatures can cause ice formation, these conditions do not specifically address the risk associated with the initial rainfall, which is particularly hazardous. Similarly, while roads may become slick after a long dry spell due to buildup, the immediate effects of the first rain offer a unique danger that necessitates driver awareness.