There are three types of movable railroad bridges: swing, bascule, and vertical lift. Georgia has examples of all three and here on the Chattahoochee is an example of vertical lift technology.
In general, vertical lift railroad bridges permit a wider passage for river traffic than swing or bascule bridges. Swing bridges, for example, must be placed in the middle of a channel, effectively cutting it in half. A major disadvantage of vertical lift bridges, however, is the limited vertical clearance. At this crossing it was determined that width of the channel was more important than boat height.
The Army Corps of Engineers maintains a navigable channel of 100 feet by nine feet on the river as far north as Columbus. When the water level of Lake Walter F. George (this bridge is at that lake's upper end) is at 185 m.s.l., the vertical clearance below the raised span is 42 feet.