why, during a snow or other wintery weather, do overpasses and bridges freeze up and become slippery first

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why, during a snow or other wintery weather, do overpasses and bridges freeze up and become slippery first

In: Chemistry

They can lose heat from underneath as well as on top so they cool more quickly. Normal roads are insulated from below by the ground but cold wind blows underneath an elevated section of road.

Cold air is able to flow both above and below the bridge/overpass, creating colder road conditions than that of a regular road.

The ground retains heat/acts as an insulator and will slow down the freezing process. In extremely cold locations, not even that will prevent roads from freezing over.

I have no idea either. But from my knowledge, I think it’s because they are extended above the ground. The higher, the colder the air is with a breeze adds to that as well since its constantly getting hit with that. Combine all that together with any little amount of precipitation, that just may be part of the reason.

Edit: downvote me. although above everyone else above has similar answers lol

Because air flow from both the top and bottom allows heat to dissipate faster than a normal road surface. A couple feet underground (varies depending on your location and time of year) the ground remains a constant ~55°.

Earth is a good insulator, it takes a lot longer for it to cool down than the air above it. An ordinary road will have cold air about it and warm earth below.

An elevated road has cold air above and below it, and is cut off from the earth’s reservoir of heat, thus will low heat much more quickly. Also, if the road is above a body of water, the air will be more humid and ice will form more quickly.