When are roads the most slippery?

The reason why roads are most slippery when it first starts to rain is due to the combination of water and the oils and pollutants that have accumulated on the road surface. When rain first begins to fall, it mixes with these substances, creating a slick layer that can significantly reduce traction for vehicles. This initial rain can cause the road to be more hazardous than during prolonged rain, where the oils are washed away, leading to better grip by tires.

As rain continues, the road often becomes less slippery since contaminants are washed away over time, and the surface may become more stable. Understanding this phenomenon is crucial for drivers, as extra caution should be exercised during that initial rain period when slippery conditions are most likely.