The most common movable bridge today is the bascule bridge. When bascule bridges open, they do so by pivoting on a fixed axis, which permits them to split into two parts that move away from each other. An open bascule bridge resembles a book when you open it at the middle. Not surprisingly, therefore, the two sides of an open bascule bridge are referred to as "leaves."
Two notable examples of a bascule bridge are located in Portland, Oregon. One is the Broadway Bridge and the other is the Burnside Bridge.
Swing-span bridges spin on a center axis. When they open, they spin horizontally until the bridge is perpendicular to its regular position. Opening in this manner creates two channels for boats to pass through. They are not terribly popular anymore because it takes too long to open and close them and doing so brings traffic to a crashing halt. It also requires too much space to open and allow boats to pass.
A notable example of a swing-span bridge is located in New York City. The bridge is on 207th Street over the Harlem river.
