The name "San'in Honsen" actually refers to 673, 8 km of railway line that is not traversed by any train in its full length. "San'in" 山陰means "the shady side," or the "cold side" of the mountain range that makes up western Japan's main island Honshû. San'in is the region along the Japan Sea coast, and it is often symbolised by the setting sun; photographs of the setting sun over the Japan Sea or Lake Shinji in the Matsue - Izumo region are often used to draw attention to this part of Japan. By contrast, the other side of the central mountain range of western Japan is called the San'yô 山陽, that is "the sunny side," or the "warm side" of the mountain range, extending from the Bay of Ôsaka all along the Inland Sea down to Shimonoseki.
The San'in Honsen can be divided into several segments, with trains operating either within one segment, or linking two segments.
Segment 3 (Izumo – Shimonoseki) is best again divided into three sub-segments, namely a) Izumo to Masuda (129, 9 km), b) Masuda to Nagato-shi (85, 1 km), and c) Nagato-shi to Shimonoseki (approx. 77, 7 km; at the very end of this sub-segment trains run over the San'yô Honsen). (Note: the suffix –shi as in Nagato-shi stands for "town".)
Sub-segment a) follows the San'in coast throughout and is served by local and accelerated as well as express trains that partly continue over the pass along the Yamaguchi-sen to Shin Yamaguchi, providing a connection there with the San'yô Shinkansen. In the opposite direction express services from Shin Yamaguchi give good access to the western San'in region.
On its way west of Izumo and past the service point of the electric sets off the Hakubi-sen the train continues to the town of Ôda, from where one can catch a glimpse of the volcanoes in the Sanbesan area. After a long coastal stretch through fishing villages the next slightly larger town is reached, namely Gôtsu with its prominent pulp mill. As from April 1, 2018, the Sankô-sen, which started at Gôtsu and ran up to Miyoshi (108, 1 km) closed to all traffic. After Gôtsu the train runs through the town of Hamada, and, continuing along the coast, through Okami to the junction at Masuda. Fly ash trains originating on the Mine-sen used to reach Okami power plant via the Yamaguchi-sen until 2014. Except for express train passengers going towards Yamaguchi it is necessary to change at Masuda, either to the stopping trains of the Yamaguchi-sen, or to the San'in Honsen trains of sub-section b), Masuda to Nagato.
The coast line between Izumo and Masuda has been interrupted many times on account of severe storms and flooding. Particularly the tragedy of July 1983 with over a hundred people killed and over 200 injured in the Hamada – Miho Misumi area remains in memory. 2013 also saw severe interruptions of services.
Construction of the line from Izumo to Masuda took place gradually between 1913 and 1923, when through services to the Yamaguchi-sen became possible. Freight services ended in the Hamada area in 1982, through freight from Izumo ceased in 1987, with Gôtsu – Okami remaining until 1997 (except for the fly ash train).
The timetable in 2018 shows stopping trains Izumo – Hamada about every 2 hours, 5 accelerated trains stopping only at the more important stations and running through from Yonago to Masuda, and 6 express trains from Tottori, and 1 from Yonago; three of these run through to Shin Yamaguchi.
Sub-segment b), Masuda to Nagato-shi: From Masuda onwards along the coast traffic dwindles to a trickle, and usually a single short railbus type diesel car is enough to handle the traffic.
Trains curve in and out of the many quiet bays and inlets, stopping from time to time in little fishing villages such as the particularly charming localities of Ii (opened in 1964) or Sammi. The major intermediate station is Higashi Hagi (Hagi East), serving the town of Hagi. Hagi was once an important castle town, famous for its samurai (warrior) district. In Hagi some of the most important and influential personalities of post-1868, post-feudal, imperial Japan were educated. Also, some of the earliest reverberatory furnaces in Japan were set up here in 1856 for casting iron canons. Hagi castle itself was dismantled in 1874.
As in other parts of the San'in, also this part of the line saw several serious landslide and flooding disasters, for instance in 1980, 2013 (Nako to Susa only reopened more than a year later, in 2014), and 2018. Freight ended 1987.
Construction of the line from Masuda to Nagato was undertaken between 1925 and 1928 (Masuda to Susa), 1924 to 1929 (Nagato to Nako), 1931 (Nako to Utagô), and through running all the way to Shimonoseki became possible with completion of the Susa to Utagô section in 1933.
All trains between Masuda and Nagato are stopping trains, a few in the morning and evening run all or part of the way, 1 train in the morning comes through from Shimonoseki to Masuda. However, during the daytime regular services are provided only once Higashi Hagi – Nagato and back, once Nagato to Utagô and back, and once by a through train Masuda to Nagato. Extra trains on some weekends operate between Nagato and Higahi Hagi.
Sub-segment c), Nagato-shi [Nagato Town] to Shimonoseki: After leaving Nagato in western direction, the train runs along the scenic inlets of Fukawa and the bay of Yuya before crossing a mountain range and turning south. Then Hibiki-nada is reached, that is the sea off the western shore of Japan's main island Honshû, directly facing the island of Tsushima and South Korea. Many of the services coming up along Hibiki-nada from Shimonoseki end or start at Kogushi, the northern limit of a somewhat busier section of the San'in Honsen. Slightly north of Hatabu (one stop north of Shimonoseki terminus), the San'in Honsen trains join the San'yô Honsen for the rest of their journey. Until 2005 there were through trains from Kogushi beyond Shimonoseki through the Kanmon Tunnel to Kokura on the island of Kyûshû.
The timetable for segment c) shows that all trains are stopping trains, with one train approximately every hour from Nagato to Kogushi (of which 3 through trains to Shimonoseki), and two more from Nagato only to Takibe. However, a more frequent service between Shimonoseki and Kogushi is provided.
Through running from Shimonoseki to Kogushi became possible in 1914. The rest of the line between Kogushi and Nagato took shape between 1925 and 1930. Freight services ended in 1986.
