There are three basic types of movable bridges; the bascule, the vertical lift and the swing bridge. Multnomah County operates four movable bridges: one vertical lift and three bascule. Swing bridges are much less common today.
The Hawthorne Bridge, crossing the Willamette River in downtown Portland, is an example of the vertical lift bridge. Other examples in the Portland area are the Burlington Northern/Sante Fe Railroad Bridge over the Willamette River near St. Johns, the Union Pacific Railroad Steel Bridge in downtown Portland and the twin I-5 bridges over the Columbia River connecting Portland with Vancouver, WA. All of these bridges have an interior lift span section that remains horizontal as it is raised upward, allowing river traffic to pass beneath the structure.
Bascule bridges have sections that rotate upward and away from the centerline of the river, providing clear passage for river traffic. Side-by-side on the Willamette River in downtown Portland, the Morrison and Burnside bridges are two examples of bascule bridges. These two bascule type bridges have a very clean, uncluttered look to them because the counterweights and operating machinery are located out of sight in the piers supporting the bridge. The Morrison Bridge is a Chicago-type bascule bridge and the Burnside Bridge is a Strauss-type bascule bridge.
The Broadway Bridge, located further downstream near the Rose Quarter, is an example of a Rall type bascule bridge. With this Rall type bascule, the counterweights are located above the roadway and much of the machinery is located in sheds, also above the roadway.
There are also several swing bridges on the Columbia and Willamette rivers. These bridges are mostly railroad bridges. Interesting examples include the Burlington/Santa Fe Railroad Bridge over the Columbia River at Vancouver, WA and the Columbia Slough near N. Columbia Blvd. A relatively new swing bridge built in the 1990s is located at the U.S. Army Corps of Engineers’ Bonneville Dam where it carries the main access road across the front of the new navigation lock. Because of the excessively long time to operate a swing bridge, many older bridges were replaced with bascule or vertical lift bridges.