# Why do bridges freeze before the rest of the road?

**URL:** <https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909>\
**Category:** Factual Questions\
**Created:** [December 4, 2001, 10:20pm UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909 "2001-12-04T22:20:41Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![sethdallob](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@sethdallob](https://boards.straightdope.com/u/sethdallob)\
**Post date:** [December 4, 2001, 10:20pm UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909/1 "2001-12-04T22:20:41Z")

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I looked in the archives, but I couldn’t find an answer…

Why do bridges freeze before the rest of the road does? The temeperature difference would seem to be very very slight…

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**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\
**Post date:** [December 4, 2001, 10:22pm UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909/2 "2001-12-04T22:22:26Z")

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Because the road is protected in part by the Earth below it, and a bridge is chilled by the air passing over it on both the top and the bottom of the surface.

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**Author:** ![Tranquilis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tranquilis/32/3639_2.png) [@Tranquilis](https://boards.straightdope.com/u/Tranquilis)\
**Post date:** [December 4, 2001, 10:22pm UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909/3 "2001-12-04T22:22:58Z")

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Because you’ve got cold air circulating above, to the sides, and _below_ the bridge. Cools it down quite nicely.

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**Author:** ![sethdallob](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@sethdallob](https://boards.straightdope.com/u/sethdallob)\
**Post date:** [December 4, 2001, 10:23pm UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909/4 "2001-12-04T22:23:24Z")

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Couldn’t answer any faster? Jeez 🙂

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**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\
**Post date:** [December 4, 2001, 10:39pm UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909/5 "2001-12-04T22:39:04Z")

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Because the bridge does not benefit from any geothermal heating…in addition to the air circulating above and around it.

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**Author:** ![DAVEW0071](https://avatars.discourse-cdn.com/v4/letter/d/e19b73/32.png) [@DAVEW0071](https://boards.straightdope.com/u/DAVEW0071)\
**Post date:** [December 4, 2001, 11:21pm UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909/6 "2001-12-04T23:21:38Z")

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Because the sign says so. If you removed all those signs, the bridges wouldn’t freeze any faster than the rest of the road.

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**Author:** ![Hoops](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hoops/32/6408_2.png) [@Hoops](https://boards.straightdope.com/u/Hoops)\
**Post date:** [December 5, 2001, 3:01am UTC](https://boards.straightdope.com/t/why-do-bridges-freeze-before-the-rest-of-the-road/96909/7 "2001-12-05T03:01:32Z")

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The bridge does not freeze; the mind freezes.  
----the Slurpee koan