The line uses a fleet of LE-Car II series diesel railcars classified "Isumi Class 200". In December 2010, former JR West KiHa 52 diesel car KiHa 52-125, formerly used on the Ōito Line was purchased by the Isumi Railway. This was repainted into JNR standard red and cream livery before entering revenue service. From March 2012, two new Isumi Class 300 diesel cars entered service on the line. Built by Niigata Transys, these feature transverse seating and toilets. On 11 October 2012, a former JR West KiHa 28 DMU car, KiHa 28 2346, was delivered to the line. This is used in conjunction with the KiHa 52 125 car. In January 2013, a JR East KiHa 30 DMU car, KiHa 30 62, previously used on the Kururi Line was delivered to the line. In 2013, a new Isumi Class 350 diesel car was delivered. Built by Niigata Transys, this car is based on the Isumi Class 300 design, but has longitudinal seating and no toilet. Designed to resemble the former JNR KiHa 20 DMU, the car is finished in the standard Isumi Railway livery of yellow with green bodyside stipes. In June 2015, a new KiHa 20 diesel car, numbered KiHa 20 1303, was delivered. Built by Niigata Transys, mechanically it is similar to the Class 300 design, and has the same style interior with transverse seating and a toilet, but externally it was built to resemble the JNR KiHa 20 design, like the Class 350 diesel car. The livery is JNR-style red and cream rather than the standard Isumi Railway yellow used on the Class 300 and 350 cars. This unit entered service in September 2015.
History
Plans for the Isumi Line were drafted by the Railway Ministry under Railway Construction Act in 1922. However, the route already had an existing gauge human-powered tramway, which had been opened by the Chiba Prefectural government on 15 December 1912 to connect Ōhara and Ōtaki. Local opposition and the deficit situation of the existing line delayed construction, which did not begin until 1925. The tramway was bought out by the Japanese Government Railways in 1927, and the first section of the new Kihara Line was opened on 1 April 1930. The line was extended to by 25 August 1933 and to its present terminus at on 26 August 1934. As its name implies, the Kihara line was originally intended to connect Ōhara with Kisarazu. However, it was never extended further than Kazusa-Nakano. In 1954, the first JNR diesel railbus, the KiHa 10000, was introduced on the Kihara Line. Four additional stations were added on 20 June 1960. However, on 4 September 1968 the line was listed as one of 83 money-losing local lines recommended for closure. The line problems were compounded in the summer of 1970, when heavy rains washed out a portion of the track, causing a suspension of operations from 1 July through 1 October. Scheduled freight operations were suspended from 1 October 1974. On 18 September 1981, the line was again recommended for closure. After the breakup and privatization of the JNR on 1 April 1987, the line came under the control of the JR East. The Isumi Line came into being on 24 March 1988 following the transfer of the assets of the former Kihara Line to the newly formed third sector operator Isumi Railway Company. The Isumi Railway has attempted to increase revenues by selling naming rights to stations to local industries, leading to some confusion on the correct station names.
