Why might a bridge surface freeze before the adjoining road surfaces?

The reason why a bridge surface might freeze before the adjoining road surfaces is that cold air circulates both above and below the bridge. Unlike standard roadways, which are mostly supported by the ground and insulated by the earth’s surface, bridges are exposed on both tops and bottoms to cold air, allowing for faster cooling. When the temperature drops, the air moving beneath the bridge can cool the structure from below, leading to a quicker drop in temperature on the bridge surface compared to the roadways, which retain heat better due to their contact with the ground. This phenomenon can lead to the bridge becoming icy more quickly, posing a greater hazard to drivers.