viaduct

A viaduct is a bridge or series of bridges designed to carry a road, railway, or other pathway over obstacles such as valleys, gorges, watercourses, or urban areas. It typically consists of multiple spans supported by piers or arches, forming an elevated corridor across the terrain below.

The term viaduct derives from Italian viadotto, from via meaning “road” and ductus meaning “led.” Viaducts have been built in many materials, including stone, brick, reinforced concrete, and steel. In older structures, arched spans are common, while modern viaducts frequently use girder, truss, or cable-supported systems and can carry single or multiple decks.

Construction and design considerations focus on providing adequate clearance, load capacity, and durability while managing foundations on various soil conditions. Design must account for seismic activity, wind, drainage, maintenance access, and environmental impact. Viaducts may be built as continuous structures with uniform spans or with varying span lengths to accommodate terrain and hydraulic or urban constraints.

Viaducts are used to keep transportation routes at grade with the surrounding landscape, minimize disruption to watercourses, and maintain grade separation over obstacles. They are common on rail networks and highways, especially in mountainous or urban settings, and can be aesthetic components of a landscape.

Notable examples include the Ribblehead Viaduct in England, a 24-arch stone railway viaduct completed in 1875, and the Millau Viaduct in France, a large modern road viaduct spanning the Tarn valley and completed in 2004. These structures illustrate the range of viaduct design from historic stone arches to contemporary reinforced concrete and cable-stayed systems.