Consider how long it would take to cross a river today if bridges were not included in the road systems. Consider how the movement of people, goods, and services would be affected without highway systems, which include bridges. The entire American economy as we know it would be stifled.

The earliest bridges consisted mainly of logs that had fallen or were placed across rivers. While inexpensive, they were less than reliable. Moving heavy loads across them was often impossible.Primitive bridges were nothing more than a cable of rope stretched across a river.

While suitable for foot travel and pack,- animals, motorized traffic would have an impos- sible time crossing it. Imagine the effects of high winds on a rope suspension bridge like the one shown.

The stone arch bridge design is among the strongest and most durable. Stone is a naturally strong and enduring material for a bridge. In stone arch bridges, the stones are in compression (pressing against each other). The costs for labor and for transporting stones for these types of bridges are great. The bridge shown in Figure 4 was built during the time of the Roman Empire nearly 2,000 years ago.Steel arch bridges are also capable of covering great spans and bearing heavy loads. The bridge in Figure 5 is 1,652 feet long. Note the cable suspended from the arch to the roadbed. This bridge is a combination of the arch, truss, and suspension bridges. In this case, the steel arch is under compression and the cables holding up the roadbed are in tension.

Steel truss bridges like the one shown in Figure 10 are not as capable of great spans as other bridge designs. However, they can be quickly assembled, or even prefabricated, and can support great loads. This type of bridge is used

Some topics in this essay:
History Bridges, Bridge California, Roman Empire, Washington Bridge, York City, River Canada, Quebec Bridge, shown figure, suspension bridges, heavy loads, bridge shown, George Washington, moving heavy loads, bridge shown figure, 1800 feet, suspension bridge, cantilever bridges, suspension bridges steel, truss design, george washington bridge, moving heavy, capable covering spans, center section,