Artificial Structures

a term used to designate transportation structures (on railroads, highways, and city streets) erected at crossings of rivers, ravines, mountain ridges, and intersecting roads. The term “artificial structures” is arbitrary; it came into use because of the complexity of construction of such structures as compared with the strips required for railroad lines, highways, and city streets. The most widespread artificial structures on railroad and motor-vehicle roads and streets are bridges, viaducts, overpasses, trestles, drain conduits under embankments, and drainage and diversion ditches. Artificial road structures also include tunnels, avalanche-prevention areas and snowsheds, retaining walls, and other special structures erected on mountain roads.

Artificial structures in cities include transportation tunnels and overpasses to separate traffic into various levels, as well as elevated and underground pedestrian crossings. Artificial structures on highways and in cities are mainly built of reinforced concrete. The cost of the artificial structures is 10–15 percent of the total cost of a road. For modern expressways, which intersect all crossroads on overpasses or underpasses, and for mountain roads and railroads, the cost of artificial structures reaches 30–40 percent.