Why are roads especially slippery right after it begins to rain?

Question

In rainy weather, roads are often at their most slippery when the rain first begins to fall. Fresh rainwater mixes with oil and grease on the road to form a slick film. As the rain continues, this mixture will eventually wash away.

Accepted Answer

The water mixes with oil and grease on the road.

Answer

Roads are naturally slippery.

Answer

Gravel often gets washed to the middle of the lane.

Answer

Tires are not usually designed to drive in rain.