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a bridge built at the intersection of two or more main transportation arteries that allows for the free flow of traffic on different levels. Overpasses are commonly constructed where highways and railroads intersect or over city streets that have both heavy vehicular and passenger traffic.
An overpass can be either rectilinear or curvilinear, dependent on the type of intersection or the configuration of the intersecting city streets. Sometimes overpasses are arranged in several tiers and their spans are located one above the other. Most overpasses are either beam or frame structures because it is necessary to keep the spans low and because of the limited space that is available for piers; arch structures are comparatively rare. Currently, most overpasses are built from precast reinforced concrete. They usually consist of two to four spans, each 10–30 m long. Overpasses with more than four or five spans are called viaducts.