stations, at Torbjørnsbu and Rossedalen, were taken into use on 1 May 1911. The same year, parliament decided that the Arendal Line would be its own district and not be administrated along with the Setesdal Line from Kristiansand. The decision to extend the line to Tveitsund (Treungen from 1926) was taken by parliament on 20 July 1908. The details for the section in Bratsberg was taken in 1910, and the remaining part in 1911. Construction started in late 1910 in the north, while the southern part started construction at the end of the year. About 300 people worked on the line, which saw a strike from 1 May 1912 until the end of August. Laying of track started during late 1912. North of Gaukås, the terrain was more hilly. At one place, of earth and needed to be removed to create a cutting. The line had a minimum curve radius of and had gravel ballast. The permanent way was built wide enough for the line to be converted to standard gauge. The long section from Åmli to Tveitsund was officially opened on 14 December 1913. However, the station buildings were not yet ready, and dispatch of passenger and freight was at first done from sheds. The stations were gradually completed by 1914. All trains running to Åmli were extended to Treungen, and the line received some new rolling stock, including two Class XXIIId locomotives. The whole railway from Arendal to Tveitsund cost NOK 9.9 million. Narrow gauge operations At Tveitsund, the railway corresponded with the ferry Nissen and Dølen, which ran on Nisser. The Nissedal Municipal Council stated that the location of the station was problematic, as it was located on the south side of the river, while most access was from the north side. A bridge across the river was therefore built and opened in 1918. In 1916, a mine was opened at Søftestad on Nisser. The ore was transported by barge down the lake and transshipped to the railway. The passenger service with Dølen on Nisser was terminated in 1937. After the opening of the line to Froland, NSB started operating ore trains from Froland to Arendal. The ore was mined at Gloserhei and hauled to Blakstad Station with horse. The mine halted production from 1914 to 1924, and after 1934 started using trucks, which ran all the way to Arendal. During the First World War, of apatite