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?

Question

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

Answer 1

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.