When are roadways typically the most slippery during rain?

The correct answer is when it first starts to rain. At the onset of rain, water mixes with the oil and debris that have accumulated on the roadway, creating a very slippery surface. This initial period can be particularly hazardous for drivers because the slick mixture significantly reduces traction.

As rain continues, some of this debris is washed away, which can reduce slipperiness compared to that initial moment when rain begins to fall. During a heavy downpour, although visibility and other factors become significant concerns, the roadway's slipperiness may not be at its worst since the continual flow of water helps clear some surface contaminants. After the rain stops, any remaining water may still keep the surface wet, but by that point, much of the dangerous oil and dirt mixture has likely been washed away, making conditions less hazardous than during the early stages of rainfall.