Why do bridges ice before the rest of the highway?
On a cold, rainy day, ice forms more quickly on bridges and overpasses for two reasons: • The freezing wind strikes the bridge above and below and on both sides, so it’s losing heat from every side. The road is only losing heat from its surface. Even while the temperature on the road surface is dropping, the heat underneath the road keeps it warm enough to prevent icing as temperatures in the atmosphere drop below freezing. Bridges have no way to trap any heat, so they will continually lose heat and freeze shortly after temperatures in the atmosphere hit the freezing point. • Most bridges today are built with steel and concrete, both of which are good heat conductors. Because these materials conduct heat, any heat that the bridge has moves through the bridge to the surface where the heat is lost through the air flow around it. Roads are mostly made from asphalt, which is a poor conductor of heat, and that lessens the rate of heat loss fro
