In general, the roads are most slippery just after the rain begins because oil dropped from vehicles has not yet been washed away. When it first starts to rain, the water mixes with the oil residue on the road, creating a slick surface that can be very hazardous for drivers. This is why the roads are often at their most slippery right at the beginning of the rain.
After several hours of light rain, the roads can also become slippery. The continuous light rain can mix with the oil and dirt on the road, making it more slippery over time. This is especially true if the rain is not heavy enough to wash away the residue effectively.
Just after the rain stops and the road is drying off, the road may still be slippery. Even though the rain has stopped, there can still be moisture on the road surface. This moisture, combined with any remaining oil residue, can continue to make the road slick until it fully dries off.
It's important for drivers to be cautious during and after rain showers, as the road conditions can be unpredictable and hazardous due to the slippery surfaces created by the combination of rainwater and oil residue.
