Japan's shortest railway tunnel

[KenS]

I found this by accident when looking for something else, Japan's shortest railway tunnel, the Tarusawa tunnel on JR East in Gunma. Total bore length, 7.2 meters (yes, you read that right).

Apparently the line was built during the war, as a rush job, but why they bored through the outcrop rather than removing what little stone remains above it is unclear.

<a href="http://www.youtube.com/v/VZCGlQ5_oPc" target="_blank">http://www.youtube.com/v/VZCGlQ5_oPc</a>

There's a prototype for everything.

[Martijn Meerts]

There's also the model version: http://space.geocities.jp/popoya2008/dm24.html

[WuZhuiQiu]

That's interesting. I wonder if the decision to bore may have had something to do with wartime scarcity in the sense that boring might have required less fuel, explosives, labour, and time?

[KenS]

The Japanese page I linked does refer to it as a "wartime rush job" but it seems to give the impression that nobody knows for certain why it was built that way, just that there are "several theories" and there's reference to a tree being on the preserved rock possibly being the cause, but no indication why that would have been a consideration (particularly during wartime).

[Shashinka]

I'd've thought something like this would have been day-lighted a long time ago.

[keitaro]

that is 1 awesome tunnel. May just make it onto my layout.

So that will be a 5cm tunnel 

[keiman]

Problem is Madog  has already done something similar.