A medium girder bridge is a type of bridge that is used to go over a river, lake, or other body of water. It is made of strong metal girders (long, thick beams) that are put together to make a long, strong support for the bridge. This type of bridge is often seen over highways and roads and can be quite long and tall. The girders are held together by strong cables or rods to make sure the bridge is secure and won't fall apart.