On a wet road, how should you adjust your speed compared to dry conditions?

On a wet road, you should reduce your speed by about one-third compared to dry conditions. So if traffic and conditions on a dry road would have you at 55 mph, on wet pavement you would be down around 35 mph. On packed snow, reduce by one-half. On ice, reduce by two-thirds. The reasons are stopping distance and traction: wet pavement can double stopping distance, and a heavy vehicle hydroplanes more easily than a car. Hydroplaning can begin at speeds as low as 30 mph when there is enough water on the road, and is more likely with worn tires, underinflated tires, or in puddles. Driving below the posted limit when conditions require it is not only legal, it is mandatory under the basic speed rule that applies in every state.