viaduct

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A series of spans or arches used to carry a road or railroad over a wide valley or over other roads or railroads.

from The Century Dictionary.

• noun An extensive bridge, consisting strictly of a series of arches of masonry, erected for the purpose of conducting a road or a railway over a valley or a district of low level, or over existing channels of communication, where an embankment would be impracticable or inexpedient; more widely, any elevated roadway for which artificial constructions of timber, iron, bricks, or stonework are established. Compare aqueduct.

from the GNU version of the Collaborative International Dictionary of English.

• noun A structure of considerable magnitude, usually with arches or supported on trestles, for carrying a road, as a railroad, high above the ground or water; a bridge; especially, one for crossing a valley or a gorge. Cf. trestlework.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A bridge with several spans that carries road or rail traffic over a valley or other obstacles.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun bridge consisting of a series of arches supported by piers used to carry a road (or railroad) over a valley