Hardturmviadukt, Railway bridge in Zürich, Switzerland

The Hardturmviadukt is a 1126-metre railway bridge in Zurich with a Y-shaped plan: a double-track section from the Käferbergtunnel to the Herdern junction, a single-track branch to Altstetten (Hardturm I), and a double-track continuation to the main station (Hardturm II). It crosses tracks, industrial land, streets, two tram lines and the Limmat, with a maximum span of 43 metres over the river.

The viaduct opened in 1969 as Switzerland's longest railway bridge at that time and was the first structure worldwide to use concrete hinges in its design. The bridge lost its length record in 2015 but remained a significant example of post-war infrastructure.

The viaduct carries the Käferberg line, which links Oerlikon station with Altstetten, Hardbrücke and Zurich main station. Its western branch, Hardturm I, opened in 1969 mainly for freight; the eastern double-track section, Hardturm II, followed in 1982 with the new Hardbrücke stop. The Y-shaped junction at Herdern is visible from the tracks.

The viaduct spans the Industriequartier between the Käferbergtunnel and the Limmat, crossing tracks, streets and two tram lines. It is best viewed from the ground along these streets; the structure itself carries railway tracks and is not a walking route. The Hardbrücke station, opened in 1982, lies near the eastern section.

Since 2005 the bridge has been illuminated at night and is part of an urban lighting project. This lighting system transforms the concrete structure after dark and makes it a visual feature of the nightscape.