Why should you reduce your speed in adverse conditions such as rain, fog, or snow?

In rain, fog, snow, or ice, both traction and visibility are reduced, which lengthens the distance needed to stop and the time available to react to hazards. Posted speed limits are set for ideal conditions, so in bad weather a safe speed is often well below the limit — and driving too fast for conditions can be a violation even when under the posted limit. Drivers should slow down, increase following distance, use headlights, and avoid sudden braking or steering. Adjusting speed to the conditions, rather than the sign, is a core safe-driving principle the permit test emphasizes.