What’s the point of a covered bridge?
Bridge building technology favored stone or masonry bridges for heavy loads up until the late 1700s, when the combination of plentiful timber and engineering in the United States led to the development of the wooden trussed bridge. The problem was that the wood exposed to weather rotted.
The wooden floor of the bridge wasn’t a concern since it could be replaced fairly easily with the right size plank, but the structural members were much more difficult to repair if they deteriorated. So, utilizing the truss structure already present on the bridge, a roof was added. By the middle of the 1800s, wrought and cast iron (and later steel) started to replace wood for bridges, though often you will find the floor of the bridge still being made of wood.
Interestingly, covered bridges were a challenge in the winter, since travel in snow often meant switching from horse drawn carriage to horse drawn sleigh. Since the bridge had a roof, straw and snow would be brought in and spread over the bridge floor so sleighs could cross.
Frederick County has three covered bridges—half of the total still standing in Maryland, which once boasted 52. Local bridges include Roddy Road Bridge, Utica Bridge and Loy’s Station Bridge.