When are roads most slippery during rain?

The correct response is that roads are most slippery right after it starts to rain, primarily because the initial rainfall mixes with oil, grease, and debris that have accumulated on the roadway surface. At the beginning of a rain shower, the water lifts these substances up, creating a very slick and hazardous layer. This phenomenon can lead to loss of traction for vehicles, making it crucial for drivers to slow down and exercise caution during these conditions.

As rain continues, the oil and debris get washed away, and while roads can still be slippery, they tend to become less hazardous as more water is present to create a smoother surface. Additionally, once the rain stops, the conditions can vary depending on factors such as the temperature and the amount of moisture remaining on the surface, but it's generally not immediately after the rain has stopped that roads become slickest. Heavy rain can create different conditions, but it is the very start of rain that presents the most immediate risk due to the interaction of water with surface contaminants.