SHEARER'S Bridge, PA

An historic covered bridge in Pennsylvania where in 1847 it was built with Birch wood using a single arch and some bolts to cross a creek near Manheim. A covered bridge was covered because they are made of wood and the roof or cover would keep the wood structure sound for over a century whereas an uncovered bridge would only last about 20 yrs. but what about railroad bridges, why aren't they covered? practicality and size. today RR trestles are made with creosoted wood to prevent as are the ties under the tracks. That started in the late 1800s. the bridges and trestles would be maintained and replaced by steel before any of them could rot.