Understanding Why Bridges Freeze Faster Than Regular Roadways

Many residents of the southern U.S. were caught off guard when a rare winter storm roared through the region that is not used to dealing with wintry precipitation. While those living in the northern half of the U.S. typically know how to handle dicey road conditions, it was a different situation for motorists along the Gulf Coast this week. One thing that is key to remember when taking on the roads during times of winter weather is that bridges generally freeze before non-elevated surfaces. But why is this? Here is a primer on driving on bridges.

Higher Exposure to the Harsh Elements

The most common reason why bridges experience freezing conditions before roads is because there is nothing solid beneath them. A lack of something concrete shielding the structure from bitterly cold temperatures makes it more susceptible to taking on the elements.

This compares to a road that is built on top of the ground. The soil serves as a source of insulation for the roads. Despite cold temperatures circulating above the roadway, there is a source of warmth beneath it that works to slow down the freezing process.

Location Over Water

In addition to being exposed on all sides, bridges also stretch across bodies of water in most cases. Regardless of if a bridge is covering a river, a creek, or a small stream, the water below will freeze quickly and send cold air flowing up to the bridge. The presence of these pockets of cold air makes the bridge more vulnerable to freezing than a normal road that is not hovering over a body of cold water.

Construction of Bridges Conducts Heat

Lastly, bridges are more likely to be the first structures to freeze, simply due to how they are made. Most bridges are made with metal or steel, known conductors of heat. While there is heat circulating within the bridge, this warmth naturally flows up to the surface, where it comes into contact with the frigid temperatures. A temperature reading of 32 degrees or below means that the warm air on the surface will freeze more quickly, creating icy spots on the bridge.

In contrast, most roads are made with a mix of concrete and asphalt. Neither of these materials is known for their ability to conduct heat. This means that any warmth under the road remains in place because it is not transferred to the blacktop. This is why it is so important to slow down when approaching bridges, even if the stretch of roadway leading up to it is dry and clear

How to Stay Safe When Driving on Icy Bridges