A wet roadway is most slippery when?

The correct answer is that a wet roadway is most slippery when the rain first begins. This is due to the interaction between water and the substances on the surface of the road. Initially, the rain mixes with oil, dirt, and debris that have accumulated on the roadway, creating a slick layer that reduces traction significantly. This combination makes the road particularly hazardous when the rain first starts, as drivers may not yet be aware of the change in road conditions.

As the rain continues, it tends to wash away much of the oil and debris, which can reduce the slipperiness of the road over time. During heavy rainfall, while the road can still be slippery, the immediate dangers posed at the very beginning of the rain are often greater due to the mixing of water with surface contaminants. After it has rained for a long period, the road may become less slippery as the surface is cleared of oil and debris, and water begins to pool rather than mix in with road grime.