The arch bridge design is one of the oldest in the U.S. Most are still standing, a testament to the strength of the design. Much of the weight is borne by abutments that begin at each end and travel along the curve of the arch. These bridges are mostly 200 to 800 feet long. The roadway can be placed on top of the arches or suspended from the arches at the bottom of the bridge.
A beam bridge is nothing more than a flat bridge that's supported by piers or pylons at either end of the expanse. These bridges are usually less than 250 feet long and are constructed of steel and concrete.
As the name implies, cable-stayed bridges feature cables that are attached to the roadway and extend upward to the bridge's narrow towers. Either the cables are attached at the top of the towers or at various points down the towers. They are then attached to the roadway at intervals throughout the entire expanse of the bridge. These bridges can be anywhere from 500 feet to nearly 3,000 feet long.
Covered bridges typically span small rivers and streams and are less than 200 feet long. Most have a roof over their entire expanse, as well as side panels to protect the roadway from snow and rain. You'll find many of them in farm country.
Suspension bridges have towers wider than the roadway. Huge cables run the entire expanse and are attached to the towers. They are then secured at both ends of the bridge on anchorages. To make the bridge even more secure, trusses are often placed underneath the roadway to prevent movement. These bridges often have a span of a mile or more, making them the longest in the world. A couple famous examples are the Golden Gate Bridge in San Francisco and the Brooklyn Bridge in New York City.
Draw bridges, also known as bascule bridges, are moveable bridges that allow boats to pass under the roadway. This is done by raising one or two sections via a counter-weight at the base of the bridge.
