extension to Olpe, five pairs of passenger trains ran between Siegburg and Olpe and four more between Siegburg and Bergneustadt.</ref> In 1910, the still operating section between Overath and Cologne was completed, ending through services between Siegburg and the Oberbergische district. This had a negative economic impact on Siegburg, because passengers now took the shorter, direct route to Cologne. The travel time from the Bergisches Land to Cologne was shortened to one and a half hours by the elimination of the detour via Siegburg and the old Siegburg–Overath route lost its importance. Between 1910 and 1914, the line was relaid in many places on the hillside, as there had been many fatal traffic accidents and complaints of noise pollution in the area between Osberghausen and Derschlag. Between Niedersessmar and Derschlag the old track was used by passenger and freight trams operated at lower speed by the Gummersbach Light Railways (Gummersbacher Kleinbahnen). Between Vollmerhausen and Niedersessmar the old track was completely removed. In 1913, a line was proposed to Eckenhagen. This 6.9 km long line was approved in March 1914, but the outbreak of the First World War, prevented its construction. Similarly, it was proposed in the 1920s to extend the Gummersbach Light Railways to Eckenhagen. Weimar Republic to the end of the Second World War The high reparations required by the Versailles Treaty led to a shortage of rolling stock and a limited timetable. But the occupation of the Ruhr in 1923, when the French occupied the Ruhr region, meant that it became an important route for diverted coal trains. Thus the Agger Valley Railway towards Olpe along with the Wiehl Valley Railway and the Wisser Valley Railway (Wissertalbahn) and its connection to the Volme Valley Railway was one of the main lines in the new Weimar Republic for a few months. Due to the large amounts of heavy trains that ran on the line to the east, the cheaply built superstructure was damaged. The repairing of this damage took some time. In 1927, a direct service to Cologne was opened. In this case, however, the Volme Valley Railway connection to the north was preferred to running to Olpe. Express trains to the north in 1931 included a connection from Wuppertal over the Wipper Valley Railway (Wippertalbahn), the Volme Valley Railway and the Agger Valley Railway to Olpe. During the construction of Agger Valley Dam (Aggertalsperre) there was a high