I’m assuming it has something to do with how thick the surface is? I see the sign that says this a lot when I drive and I want to know why. I was even stumped a while back when my nephew asked why because I didn’t have an answer
In: Planetary Science
Because air can flow under the bridge as well as above it, so the surface can cool more/faster
The ground tends to hold its temperature better than the air, so when a road is on earth, only one side is in the freezing air, the other is insulated by the soil.
A bridge will not have this insulation. It has freezing temperatures above and below it, so it will be colder, and ice will form there first.
No insulation (ground) underneath it. Bridges are often near or over which will increase ice buildup from the moisture.
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