What Makes Icy Bridges So Dangerous?

Jan Wesner Childs
Published: November 7, 2019

With winter weather already here for much of the United States, officials are warning drivers to beware of bridges that ice over before roadways.

The image above, taken by a drone in Flint, Michigan, shows how dramatic the difference can be between perfectly clear roads and an icy bridge.

But what causes the phenomenon?

"Bridges often freeze first and stay frozen longer because elevated surfaces are unprotected from the elements and aren't able to take advantage of the warm ground," weather.com meteorologist Jonathan Belles explained. "Wind often funnels under bridges, chilling the air and keeping those roadways colder than they would be otherwise."

A frozen overpass is seen on the morning of Thursday, Nov. 7, 2019 in Flint, Michigan.
(Image courtesy of Isaac Scharrer)

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The difference can take drivers by surprise.

"This phenomena often catches drivers off-guard when they transition from a dry, warm road to an iced-over bridge, often losing control of their vehicle sometimes long after ice melts or well before ice forms on other surfaces," Belles said.

At least two deadly accidents and one resulting in life-threatening injuries have occurred in the past few days after drivers lost control of their vehicles on icy bridges. Two people died in a crash Thursday morning on a bridge in St. Clair County, Michigan, north of Detroit on the Canadian border, according to the Associated Press. Two people also died on an icy bridge in Iowa over the weekend, the AP reported.

Two people sustained life-threatening injuries after a driver lost control of a vehicle on an icy bridge in South Dakota. The state highway patrol said the incident happened Tuesday afternoon on Interstate 29 about an hour north of Sioux Falls. The driver crossed the median into the path of an oncoming semi truck after hitting a patch of ice. The vehicle was destroyed.

The same conditions that cause icy bridges can also cause another potentially deadly winter driving threat.

"This wind also creates an invisible danger – black ice," Belles said. "With temperatures slightly above freezing near the ground, most people assume that water on roadways will remain in liquid form. But the extra wind can drop the temperature and turn a thin layer of water to ice that motorists cannot see when they are driving toward and over an overpass."

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.


The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.