What creates the most slippery road conditions during the early stages of rain?

The mixing of water with dust, dirt, and oil creates particularly slippery road conditions during the initial stages of rain because it forms a slick layer on the road surface. Before a significant amount of rain falls, the oils and contaminants on the road do not have enough water to wash away completely. As rain begins to fall, it combines with this layer, creating a very slippery film that reduces traction for vehicles. This phenomenon can lead to a greater risk of skidding and loss of control, especially for vehicles that are traveling at higher speeds or have worn tires.

While heavy rainfall can create dangerous conditions later on, it often helps to wash away the oils and debris and can ultimately improve traction after some time. The road surface temperature plays a role in how quickly water evaporates or how well it mixes with debris, but it does not directly cause slipperiness in the same way that the mixture of water, dirt, dust, and oil does. Similarly, the presence of snow presents its own challenges, but it is not relevant to the conditions created by the initial rainfall.