Winter road travel can be hazardous and unpredictable, particularly when drivers encounter patches of ice. A bridge surface can suddenly ice over even after its predecessor roadway has been cleaned and salted; making it hard for drivers to regain control as they cross it. But why does this occur?
Many drivers may have come across the phrase, "Bridges Ice Before Roadways", and wondered why. This phenomenon occurs for several reasons; first being that roads can benefit from insulation from the ground which allows them to remain warmer for longer than other surfaces compared with bridges where frozen air flows over them from both directions, making bridges more likely to freeze quickly than roads.
Bridges are often constructed of materials like steel and concrete that serve as effective conductors of heat, dissipating its warmth quickly. When air passes over and under a bridge it quickly loses heat into the surrounding air, quickly cooling it faster than roads with asphalt pavement retaining warmth more effectively than bridges do.
Bridges also boast greater surface areas than roadways, making them more exposed to the elements from all directions than roadways which only have two exposed surfaces. Heat loss occurs through air above and energy gained through contact with warm ground below; thus slowing the cooling process and keeping roads warmer than bridges.
Given these circumstances, bridges tend to become icy faster than roadways and may even become the first surface drivers encounter when entering an intersection, potentially catching drivers by surprise and leading them down an unexpected route that results in crashes even when the roadway below appears clear.
Though this phenomenon may seem harmless, drivers should still exercise extreme caution when travelling on bridges as multiple patches of ice may not be readily noticeable. It can become particularly hazardous when moving from smooth asphalt roads onto rough and icy bridge surfaces when changing lanes onto said bridge. Therefore, drivers must pay careful attention when entering or leaving roadways or bridges that run alongside them - our blog offers more details and safety tips related to winter driving safely.