When are highways most slippery?

Highways are most slippery when it starts to rain because the rain can create a layer of water that mixes with oil and dirt accumulated on the road surface. This combination reduces traction for vehicles, making it particularly dangerous. The initial rain can be especially slick as it has not had much time to wash away the oils and debris from the pavement.

In contrast, during dry seasons, the roads tend to have better traction unless they are covered with dust or sand. Heavy snowfall presents its own challenges but usually results in snow-covered surfaces, which can also be slippery, albeit in a different way. In the middle of summer, roads tend to be dry and warm, which generally provides better grip for vehicles. Therefore, the transition period when it first begins to rain is the most critical time for slippery conditions on highways.