Why is it only bridges that have a warning sign of freezing and slipping when it’s below a certain temperature, but regular roads don’t have that sign?

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Why is it only bridges that have a warning sign of freezing and slipping when it’s below a certain temperature, but regular roads don’t have that sign?

In: Physics
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When it’s cold you may have seen the river/water start to steam up. This greatly increases the humidity around the bridge.

Now, the bridge, unlike the ground, is exposed to the air on 4 sides. This means it cools MUCH faster than the rest of the highway.

This causes the humidity in the air to freeze to the cold surface, in this case the bridge deck. It’s basically a much larger version of your car windows fogging up from your breath.

The ground is good insulation, so roads are only getting the cold air from one side, while the (relative) warm dirt below keeps the road warmer. Bridges are surrounded by that cold air and thus drop in temp more quickly toward the frigid air temp.