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Viaducts are bridges designed to cross land and can be used for cars, pedestrians, cyclists, trains, and trucks. They are commonly used in valleys and areas with overlapping traffic flows. Viaducts can be made of stone, brick, metal, or concrete and are often considered aesthetically valuable.
A viaduct is a bridge constructed from a series of spans and designed to cross land, rather than a body of water. Viaducts can be used in a wide variety of ways, and numerous examples of this type of bridge design can be found around the world, made from a variety of materials. Viaducts have been built since ancient times to carry pedestrians and wagons, and today they can be used for cars, pedestrians, cyclists, trains and trucks.
A common site for viaducts is in the valleys. Constructing a viaduct allows a road or railroad to cross a valley or chasm quickly, rather than forcing engineers to carve a path for the bottom of the road to reach the valley floor and then establish a route out of the valley. While building a viaduct can be very expensive initially, it is generally cheaper and safer than keeping the road level.
A viaduct can also be used in an area where different traffic flows overlap, allowing traffic to pass over and under the viaduct so as to reduce traffic disruption. Viaducts are common features in regions with many highways, accommodating multiple traffic flows without forcing traffic to stop. The construction of viaducts is also particularly common in areas where trains and cars have to travel to more or less the same places. Trains can pass under a viaduct, while cars can pass over it, or vice versa. In both cases, car traffic does not have to stop for passing trains and the risk of train/car collisions is greatly reduced.
In classic viaduct design, engineers begin by building a series of towers, then connecting the towers with arches and installing a ballast. In the case of a viaduct designed so that traffic can flow underneath, the arches must be built particularly high up to ensure that passing traffic has enough free space. Viaducts over low-lying valleys and in other situations where underlying traffic is not expected may have much lower arches, as clearance is not an issue.
Many historic viaducts are made of stone and brick, but metal and concrete can also be used. In communities with older viaducts, conservation organizations sometimes work to keep the viaduct in good condition, as stone and brick viaducts are considered aesthetically valuable. It’s also possible to find examples of derelict viaducts that were left behind when roads shifted or became impassable, and these sites sometimes become popular with walkers.
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