Swing bridges are usually divided into two parts meeting in the middle, and each moved on pivots on the opposite sides of the channel, or they may move as a whole on a pivot in the middle of the channel.
Rolling bridges are suspended from a structure high above the water, and are propelled backwards and forwards by means of rollers.
Bascule Bridge Open[53]
Bascule Bridge Closed[53]
The advantages of this type of bridge are that the entire width of the channel is available for navigation, and the draw may be opened and closed more readily than the swing type.