Agatsuma Line

Although the official start of the line is at Shibukawa, all trains run through on the Jōetsu Line to/from Takasaki.

• 115 series 4-car EMUs
• 211 series 4-car EMUs (since August 2016)

Four-car 211 series EMUs entered service on the line from 22 August 2016.[1]

• 
  A 211-3000 series EMU

The line opened on 2 January 1945 as the freight-only Naganohara Line (長野原線) operating between Shibukawa and Naganohara Station (長野原駅) (present-day Naganohara-Kusatsuguchi Station).[2] Passenger services were introduced as far as Nakanojō from 5 August 1945, to Iwashima from 20 November 1945, and to Naganohara-Kusatsuguchi from 20 April 1946.[2]

The remains of the former Ōshi Station in June 2013

On 1 October 1952, the line was extended to Ōshi Station (太子駅), initially for freight only, but passengers services were also introduced from 21 June 1954.[2] Freight services between Shibukawa and Ōshi ceased as of 1 October 1966.[2]

Services on the section between Naganohara and Ōshi were suspended as of 1 November 1970, and on 7 March 1971, a new line was opened beyond Naganohara to Ōmae, with the entire line renamed Agatsuma Line at the same time.[2] The Naganohara-Kusatsuguchi to Ōshi line was formally closed as of 1 May 1971.[2] CTC signalling on the entire line was also commissioned at the same time.

With the privatization of JNR on 1 April 1987, the Agatsuma Line came under the ownership of JR East.[2]

It had been proposed to extend the line to Nagano, but geological exploratory drilling revealed extensive faulting beyond Ōmae, and as any extension would have required extensive tunnelling, this was considered impractical.

The Yanba Dam was proposed for construction, and required the realignment of the line between Iwashima and Naganohara-Kusatsuguchi. Construction of the diversion was well advanced when a change of government in 2009 resulted in the project being halted. Another change of government in 2012 revived the project. Services on the old section of the line were suspended following the last scheduled service on 24 September 2014 to allow commissioning of the new alignment.[3] The new alignment opened for passenger services on 1 October 2014.[3] The new route was be 0.3 km shorter, and resulted in the shortest tunnel in Japan, the 7m Tarusawa Tunnel, being abandoned, although it will not be inundated by the new dam.[4][5]

The Agatsuma Line is noted for numerous onsen hot springs along the route. The famous hot springs at Kusatsu are some distance north of the line, but several rural onsen such as those at Shima, Sawatari, Kawarayu, and Shiriyaki are more accessible.

Mount Asama, Mount Kusatsu-Shirane, and the Agatsuma Canyon can all be seen from the Agatsuma Line, though the canyon will be inundated when the Yanba Dam is commissioned.