 The mountains between Flieden and Schlüchtern initially led to the decision to build a zig zag line in order to avoid building an almost 4 km long tunnel.This required all through trains to reverse at Elm, which led to increasing congestion as traffic increased with the connection of the Flieden–Gemünden railway to the line at Elm in 1873.Tunnel-building technology had improved significantly by the beginning of the 20th century, notably with the increased availability of dynamite.