New Hampshire Driver's Education Practice Exam

Which statement explains why bridges may ice up before roads?

Bridges have less sun exposure Cold air circulates above and below the bridge Bridges are built with warmer materials Traffic warms the surface more on bridges

Correct Answer:

Cold air circulates above and below the bridge

Explanation:

The main idea is that bridges lose heat faster than roads because they are exposed to cold air on both sides. A bridge deck sits above open ground, so cold air can circulate over the top and flow beneath the structure as well. This convection pulls heat away from the surface from both directions, so the bridge cools more quickly and can reach freezing while nearby road surfaces, which are partly insulated by soil and can retain some heat, stay just above freezing. Additionally, bridges don’t have the earth to store warmth like roads do, and they shed heat to the night sky, speeding up radiational cooling. All of this means moisture on the bridge freezes earlier, causing ice to form before roads.

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