Which weather condition might significantly reduce road traction?

The correct answer is snow or ice because these conditions create a slippery surface on the road, significantly diminishing tire traction. When snow accumulates, it can form a layer that vehicles can easily slide on, while ice, especially black ice, can be nearly invisible and extremely slick. Both conditions require drivers to reduce speed and increase following distances to maintain control of their vehicles.

In contrast, heavy fog decreases visibility but does not inherently affect traction; thus, while it poses other dangers like reduced sight distance, it doesn't contribute to slippery road conditions. Sunny weather typically provides the best road traction as dry surfaces allow for better grip. Light rain may create some slickness on roads, particularly after a dry spell, but it generally does not have the same level of impact on traction as snow or ice.