was mined and transported by rail from Blakstad to Arendal. During the war, the railway increased its transport of wood, used to replace coal. The lack of coal also resulted in many cancellations on the line. In 1910, construction work started for Bøylefoss Power Station; the railway ran right past and was used for transport of both materials and people. During construction, a halt was built there. The power station was completed in 1913. Construction of Høgefoss Power Station, also located along the line, started in 1919 and was completed the following year. Later construction included Flatenfoss Power Station between 1925 and 1928, and Evenstad Power Station between 1937 and 1940. From about 1915, milk transport started along the lower part of the line. Milk weights were installed at Lindtviet, Løddesøl and Rise. From 1 July 1913 though 31 June 1914, the Treungen and Grimstad Lines had 157,986 passengers, of which 2,461 traveled on the 50% more expensive second class. By 1918–19, the ridership had increased by 10,000, while the number of second class riders was halved. From 1924, all second-class carriages were removed on both lines. The line received two Cmb 13 diesel multiple units in 1927, and a third in 1930. This resulted in additional halts being created, and for a short while the multiple units would even stop at road crossings. In 1928, NSB unmanned the stations Bråstad, Haugsjø, Vallekilen, Seljås, Sandå and Gaukås. On the express trains that ran from Treungen to Arendal in the morning and the other direction in the evening, there was a post clerk. In addition to dispatching post, he sold newspapers, magazines, lottery tickets and could be hired to perform various smaller tasks while he was in Arendal. Standard gauge In 1927, the Sørland Line was extended to Neslandsvatn and received a temporary terminus at Kragerø via the Kragerø Line. The next stage of the line was the extension from Neslandsvatn to Nelaug, where it would connect to the Arendal Line and use it to reach the coast. In preparation for the arrival, NSB had in 1923 proposed to convert the Treungen and Grimstad Lines to standard gauge. This was denied, but again proposed in 1928. The cost was estimated at NOK 2.7 million. NSB also stated that an alternative was to close the line north of Nelaug and the Grimstad Line. In 1931, a new proposal was made, and finally