Bridge Building Easier - Bridges are structures built over a river, railroad track, road, or some other obstacle. They allow people or vehicles to cross from one side to another. Harder - Bridges are structures used by people and vehicles to make crossing areas easier in travel.
Engineers build bridges over rivers, lakes, ravines, canyons, railroads, and highways.
Bridges must be built strong enough to safely support their own weight as well as the weight of the people and vehicles that pass over it. The bridge must also withstand natural occurrences that include weathering, earthquakes, strong winds, and freezing and thawing. An article from the Turner Fairbanks Highway Research Center discussing the importance of research in maintaining America's bridges. This website looks at the three major types of bridges so that you can understand how each one works. The type of bridge used depends on various features of the obstacle.