When are roads most slippery?

The first rain after a dry spell creates conditions that can make roads particularly slippery. When it hasn’t rained for an extended period, dust, oil, and grime can accumulate on the roadway surface. When the first rain arrives, it mixes with these substances, creating a slick, greasy film that can reduce traction significantly. This is especially dangerous for drivers, as the roadway can become unexpectedly slippery. Drivers should exercise caution during these conditions, as they may not realize the reduced traction until it's too late.

In contrast, roads can also be slippery after heavy snowfall, but they typically become less slippery once the snow has been cleared away. During the summer, while heat may affect road surfaces in different ways, it doesn't typically create the same immediate slippery conditions as rain on a dry road. When gravel is present, while traction can be affected, it does not have the same immediate impact on slip conditions as the interaction of rain with accumulated oil and dust.