Why bridges and overpasses get slick first


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It’s a wet and mild start to the workweek, but a the winter chill will return tomorrow and could lead to a slick drive into work.

As a cold front moves through Monday night into Tuesday, there will be a sharp drop in temperatures.

While lows by stay just above freezing in Columbus, and so should the majority of roads on Tuesday morning, bridges and overpasses could be a different story.

As temperatures fall from around 10 degrees above normal on Monday, to 10 degrees below normal on Tuesday, Road surface temperatures will start to gradually fall as well.

Surfaces like water and roads can cool at a slower rated than the air. However, elevated surfaces like bridges and overpasses can be the first to freeze.

This is because cold air is more dense than warm air, which means that it will sink to lower levels. As cold air becomes more trapped it cools the bridge or overpass to the same temperature as the air.

Icy conditions on elevated surfaces like a bridge or overpass might come as a shock to unprepared drivers because they become icy before the main road. This is because it does not have the protection from the cold and is cooling down from air both above and below the surface.

Since the change to an icy road is often not visible to drivers, they need to watch for black ice. Black ice is often just a very thin layer that has frozen as road surface temperatures drop below freezing.

Before you head out the door on Tuesday, there are a few things you can do to make sure that you have a safe drive to work. Remember sayings like “ice and snow, take it slow.” Plan for extra travel time and more stopping distance between yourself and the car in front of you. And remember that while most of the road is fine, bridges and overpasses could have spots of black ice since they cool down much faster.

Copyright 2020 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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