Whenever you get to a rapidly flowing river, you would certainly like to cross over it without getting wet. To do this, you need some form of structure that crosses over it like a bridge or viaduct. However, when you come to one of these things, it could be a viaduct or a bridge. They do the same thing.
However, there are some differences between the bridges and viaducts that you see all over the world. Bridges are conventional and may appear beautiful, or they may appear minor. Viaducts are a type of bridge. Therefore, there are many types of bridges, but there is only one type of viaduct. Viaducts usually have parts to them and may have tunnels or other bridges attached to them.