What effect does rain have on road conditions?

Rain has a significant impact on road conditions, primarily by making the road surface more slippery. When rain begins to fall, it mixes with oil and debris that has accumulated on the roadway, creating a slick surface. This slippery condition can increase stopping distances and reduce vehicle control, especially for vehicles that are accelerating or braking. Drivers need to be particularly cautious during the initial moments of rainfall, as this is when the road is at its most slippery due to the mixture of water with oils and other substances.

In this context, while visibility is indeed affected by rain and can lead to dangerous driving conditions, the primary focus of the question is about the physical conditions of the roadway itself. Rain does not improve traction; rather, it reduces it, especially when combined with other road contaminants. Hence, the correct answer highlights the primary safety concern for drivers during wet conditions.