Weather Tidbits: Why Bridges Freeze First

In this edition of Weather Tidbits, we will be discussing why wet bridges freeze first versus wet roads. Roadways are fairly protected from many weather elements aside from the freezing temperatures, but that is not the case with bridges. Most roads lose heat evenly. But unlike normal roads, which have the ground to help insulate them, bridges do not. With bridges, the cold air can flow and reach both below and above the bridges. This results in a quicker loss of heat from the bridge’s surface than a regular road. For example, both the grounded road and the bridge may start at 38 degrees. With exposure to colder temperatures, the temperature of the road may drop to 34 degrees. In that same time, the bridge surface may drop all the way to 30 degrees, which would cause any wet surfaces to freeze and create slippery driving conditions.