Translations:AY Honors/Bridges/Answer Key/71/en

A structure with enclosed sides and a roof that often has only a single lane, and typically is made of wood. Since wooden bridges tended to deteriorate rapidly from exposure to the elements, they only had a useful lifespan of nine years. Covering them protected their structural members, thus extending their life to 80 years or more. Though it would seem that covering them would also eliminate the need to plow them after snowstorms, they actually had to move snow onto them in winter so that sleighs could go through. Before automobiles, roads were compacted rather than plowed, and pulling a sleigh across an un-snowed deck would have been very difficult.