Why Covered Bridges?
The superstructure (sides, roof) was placed on the bridge to protect the understructure (bridge bed) from the weather. Since the bridges were made of wood, this protection gave the bridge a longer service life. Actually, the EXACT reason for building covered bridges seems to have been lost in time, but the weather protection arugument seems to be the most widely held. Other reasons offered have been to keep horses from being spooked by fast running rivers or as places travels could take shelter. Width was usually based on who would use the bridge. For example if it was access to a local church, it probably only need to be wide enough for a buckboard. If a trade route, then a size useful to farming, say the width of a hay wagon, would have been appropriate.
