Final answer:
Roads are most slippery at the beginning of rain, due to the mixture of light rain with oil and gasoline residues on the road. Heavy rain may improve traction by washing away the slick mixture. Caution is advised as stopping distances vary with road conditions.
Step-by-step explanation:
The roads are often at their most slippery at the beginning of the rain, particularly after a dry spell. This is because when light rain mixes with oil and gasoline residues that have not yet washed away, it creates a slick surface. If a heavy rain follows, it can eventually wash away the oily mixture, potentially improving traction compared to the initial downpour. Factors like road condition, vehicle speed, and tire maintenance also play significant roles in roadway slipperiness. It is essential to drive cautiously and consider the increased stopping distances required under rainy conditions, as illustrated in the varying stopping distances required for a car on dry, wet, and icy surfaces.