わが国における鉄道トンネルの沿革と現状 (第4報)

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The line between Takasaki and Naoetu which belonged to the old Imperial Japanese Railways, and the line between Naoetu and Niigata which belonged to the old Hokuetu Railway Company were laid in Meiji Era to link Kanto areas with Japan Sea coast. After Hokuetu Railway Company was bought by the government, these lines were designated collectively as a Shin-etsu line. This report describes the history and present state of railway tunnels, taking an example of Shin-etsu line based on field surveys and historical records. There was on this line some 26 tunnels constructed with Abt track to climb the steep section between Yokogawa and Karuizawa at over Usui Pass. The tunnels between Nagano and Naoetu were constructed in the early stage of tunnel work in Japan, and the tunnels between Naoetu and Niigata were constructed by private railways.
Through investigations of these tunnels, it has made been clear that the original tunnels were abandoned for reconstruction to be electrified and double-tracked, but most of them have remained in original forms, as a valuable heritage from the Meiji Era.