Why do bridges freeze before roads?

Some bridges have different kinds of concrete and asphalt surfacing, I think, which probably has something to do with it. I know in a few places I've lived the pavement always goes from dark asphalt to a light, ashy grey on bridges. My guess is cold and moisture treat it differently.

I always thought it was just because the bridge is farther from the surface of the earth (so it's farther from a body of heat).

	LiteStyle0o -  635 pts -  (2 years ago)
	That makes sense.

Fermat is correct. Cold air can circulate under the road surface. The temperature of the bridge will drop along with the air temp. Any moisture will quickly freeze and stay frozen as long as the air temp is below freezing. Normal road surfaces have the ground to insulate them underneath so any heat that is trapped in the ground will keep them from freezing as fast.

Also, a lot of bridges go over a body of water which means that the moisture from that area is more likely to affect the surrounding surfaces.

	LiteStyle0o -  635 pts -  (2 years ago)
	Also good sense.