Melanbogenbrücke der L143, Road bridge in Troisdorf, Germany

The Melanbogenbrücke der L143 is a 265-metre road bridge over the Sieg between Sankt Augustin-Menden and Troisdorf. Its main span is a 60-metre reinforced-concrete arch above the roadway, tied to it by concrete hangers; six flood arches of 20 to 25 metres stand on the Menden side and one 20-metre flood arch on the Troisdorf side. The deck is 10.8 metres wide.

The structure was built in 1929 using a patented method developed by Josef Melan and replaced a ferry service at that time. After damage during the Second World War, the bridge was rebuilt and returned to service in 1949.

Until the ferry was replaced, the crossing carried traffic toward Siegburg; after December 2006 around 700 lorries a day still used it, mainly suppliers to the Klöckner-Mannstaedt works and the neighbouring RSAG, Remondis and Suez waste firms. The bridge is listed as a monument of German engineering, and its name recalls Josef Melan's patent.

The bridge carries the L143 (Siegstraße) between Sankt Augustin-Menden and Troisdorf. Since December 2006 it has been closed to heavy goods vehicles over 14 tonnes; cars and limited heavy traffic still cross. During the planned demolition and rebuild, expected to take two and a half to three years, the crossing will be fully closed and traffic diverted over the B56 Siegbrücke.

Only a few Melan arch bridges were ever built; another survives at the former Arnau on the upper Elbe. The Sieg crossing is a steel-concrete composite deck with concrete hangers tied to the arch above the roadway, a rare variant of Josef Melan's patent.