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Blue Ridge Parkway tunnels consist of a total of 26 vehicle tunnels constructed along the of the Blue Ridge Parkway. One, the Bluff Mountain Tunnel,〔(Blue Ridge Parkway North ) 〕 is in Virginia and twenty-five are in North Carolina.〔(Virtual Blue Ridge tunnels )〕 The design standards specified a minimum impact on the land. The vehicle tunnels were often constructed to reduce excessive landscape scarring that open cuts would have produced. They are used in areas of steep terrain where ridges run perpendicular to the roadway alignment. North Carolina's more rugged terrain required the majority of the tunnels. Most of the work on the tunnel digging was done by hand and provided by the Civilian Conservation Corps in the 1930s.〔(Blue Ridge Parkway history )〕 Little machinery was used with the intention of creating manual labor in depressed economic times. They did have for tunneling truck-mounted water-cooled compressed air drills called "Jumbos." After the initial holes were drilled into the substrata, dynamite was used for blasting away the rock.〔(Blue Ridge Parkway tunnels )〕 Concrete lining was done during construction due to tunnel cave-ins.〔(Blue Ridge Parkway Tunnels )〕 This concrete lining was first used in the Devil's Courthouse Tunnel. It was later discovered that it enhanced the interior lighting within the tunnel itself. Where done the lining covered about a quarter of the interior structure. An additional benefit was the elimination of moisture entering the tunnel. Moisture in the winter caused ice problems.〔''Historic American Engineering Record,'' National Park Service, Jennifer K. Cuthbertson, 1997 (Sheet 1 of 28) and Lia M. Dikigoropoulou, 1997, (Sheet 24 of 28).〕 The Pine Mountain Tunnel is the longest on the Parkway at . Ferrin Knob Tunnel #1 is the first and longest of the ''triplet tunnels.'' The local people once referred to ferns as "ferrins." Ferrin Knob Tunnel #2 is located at milepost 401.3 and Ferrin Knob Tunnel #3 is located at milepost 401.5. The distinctive stone masonry portals now on the parkway tunnels were generally not part of the original construction of the 1930s. They were added later.〔(Blue Ridge tunnels - National Park Service )〕 ==Tunnels== The tunnels are listed below by milepost, name, and length. The maximum height is in the center of the tunnel and the minimum height is at the edge stripe. NOTE: This table contains data that is significantly different from that provided by the National Park Service on their Blue Ridge Parkway site. The differences are mostly in the tunnel lengths, but also some max/min tunnel heights. If you intend to drive the Parkway by motorhome, please refer to the NPS site for the correct tunnel data.〔http://www.nps.gov/blri/planyourvisit/tunnel-heights.htm〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Blue Ridge Parkway tunnels」の詳細全文を読む スポンサード リンク
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