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…
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.
Because you’ve got cold air circulating above, to the sides, and below the bridge. Cools it down quite nicely.
Couldn’t answer any faster? Jeez 
Because the bridge does not benefit from any geothermal heating…in addition to the air circulating above and around it.
Because the sign says so. If you removed all those signs, the bridges wouldn’t freeze any faster than the rest of the road.
The bridge does not freeze; the mind freezes.
----the Slurpee koan