Why is a bridge's road surface more dangerous in winter?

A bridge's road surface is more dangerous in winter primarily because it may remain icy while the rest of the roadway is clear. This occurs due to the structure of bridges, which are exposed to air both above and below, allowing temperatures to drop more significantly than on regular roadways that are insulated by the ground. As a result, moisture can freeze on the bridge deck, creating icy conditions that are not present in other areas. Drivers may be caught off guard when transitioning from a clear highway to a bridge surface that is slippery, which increases the risk of accidents.

The other situations posed, such as the bridge always being wet or elevated causing more snow, contribute less directly to the specific danger of icy surfaces. Additionally, while accidents can happen on bridges, mentioning them does not capture the primary reason for the increased hazards during winter conditions which is the ice formation.