is a bridge
that connects points of equal height in a landscape, usually by bridging a river valley
or other eroded opening in an otherwise flat area. Often such valleys have roads descending either side (with a small bridge over the river, where necessary) that become inadequate for the traffic load, necessitating a viaduct for through traffic. Such bridges also lend themselves for use by rail
traffic, which requires straighter and flatter roadways. It gets its name from an analogy with aqueduct
, which must also be practically flat, while a bridge for people, pack animals, or non-rail vehicles can be hump-backed and gain a structural advantage (i.e., less material or design sophistication needed) from that shape.
Some well-known viaducts include: