Nagarayama Tunnel (長等山トンネル)

Both Nagarayama Tunnel and Nagara Tunnel are tunnels dug through Mt. Nagara (354 m in height) between Otsu City in Shiga Prefecture and Yamashina Ward in Kyoto City of Kyoto Prefecture.
The two tunnels are:

Nagarayama Tunnel on the Kosei Line (See 'Nagara Tunnel on the Kosei Line').

Nagara Tunnel on Biwako Nishi Jukan road (Northern lakeside bypass of National Route 161) (See 'Nagara Tunnel on Nishi-Otsu Bypass').

The First Tunnel (also called Nagarayama Tunnel) of the Lake Biwa Canal (the Canal No. 1) is also described in this section.
(See 'The First Tunnel of the Lake Biwa Canal'.)

Nagarayama Tunnel on the Kosei Line

It is the railway tunnel constructed between Yamashina Station and Otsukyo Station on the JR West Kosei Line with the total length of 3,032 meters, having a special structure with three portals on the Yamashina side and one portal on the Otsukyo side and the tracks from the Yamashina side converged into one toward the Otsuryo side. Construction started on September 10, 1967, completed on April 16, 1971, and the tunnel opened in 1974, when the Kosei Line was inaugurated. Both the entry and exit points of the tunnel are ballast-tracked, while inside of the tunnel is slab-tracked. The tunnel, and also the Osakayama Tunnel (Biwako Line), belong to Otsu City.

Structure and track allocation

These three portals of the Nagarayama tunnel on the Yamashina side and the four portals of the Shin-osakayama Tunnel make the structure very complicated; therefore, the allocation of the tracks from Yamashina Station is also explained here.

Yamashina Station and the tunnel entrance on the Yamashina Side

At Yamashina Station, there are six tracks as follows: From north to south, Biwako Line (Outer track, westbound), Kosei Line (eastbound), Biwako Line (Inner track, westbound), Biwako Line (Inner track, eastbound), Kosei Line (westbound), and Biwako Line (Outer track, eastbound).

Starting from a position about 500 m off the station (the same shall apply hereinafter) with a gradient of the straight line (railway) becomes 18 (in per mille) on the eastbound track of Kosei Line, 16 on the westbound track of Kosei Line, and 10 on the four tracks of Biwako Line, and thus the Kosei Line runs on elevated tracks. Afterwards, from a position of about 1,300 m, a gentle gradient sidetrack of the eastbound Kosei Line diverges to the north of the Outer eastbound Biwako Line. From a point of about 1,600 m, the tracks of the Kosei Line intersects the tracks of the Biwako Line, and Kosei Line tracks (westbound and eastbound) proceed toward portals for westbound and eastbound located about 1,750 m from this point, with a gradient of -11 for eastbound, and a gradient of 1 for westbound. The gentle gradient sidetrack of the Kosei eastbound track, running on the northmost track, encounters a tunnel portal 1,640 m off the station.

The gentle gradient sidetrack diverging from the westbound Kosei track secures a certain nominal hauling capacity by decreasing the gradient in order to enable heavy trains to pass through. Among the eastbound tracks running on the Kosei Line, local trains and Special Rapid trains run on the eastbound tracks, and Limited Express trains and freight trains run through the sidetrack. The speed limit at the point of divergence to the gentle gradient sidetrack is 60 km/h (the same speed limit is applied at the joining point of the tracks inside the tunnel (described later)).

The tunnel entrance on the Yamashina side and Otsukyo Station

The eastbound track starts to have a gradient of 8 at about 300 m from the entrance of the tunnel (the same shall apply bellow), and immediately joins the gentle gradient sidetrack. Then, there is a section formed with left (rail) alignment, and at about 950 m from there, the track becomes straight. At about 1,100 m, the tunnel of the westbound track joins the eastbound track coming from the right, to make a double-track tunnel. Then, the tracks run on straight lines for a while, and starts running upward with a gradient of 2 from the point of some 1,900 m. From the point of some 2,600 m the tracks curve to the right hand until the portal which is 4,800 m off the Yamashina Station. After passing the exit, there is a crossover turnout, then the tracks reach the Otsukyo Station.

The westbound track goes through the same double track tunnel until it diverges from the eastbound track, and it runs downward at a gradient of 8 midway. The track curves to the left at a point about 1,800 m from the entrance of the tunnel with the radius 1,000 m, while the eastbound track on the opposite side maintains a straight line. Ahead, there is a right-hand curve with the radius 800 m, in the middle of which, the track runs downward at a gradient of 18, then beyond the curve, the track proceeds straight to the exit.

On both of the westbound and eastbound tracks, the speed limit in the section within the curve with the radius 1,400 m near the exit on the Otsukyo side is 125 km/h, and the speed limit in the section within the curve with the radius 800 m of the westbound track on the Yamashiro side is 115 km/h.


Near the junction of the eastbound track and the gentle gradient sidetrack of the Kosei Line, there is a railroad signal (the 3rd block signal) which is located in a clearly visible place seen from both of the tracks.

On the Kosei up line, soon after leaving the exit on the Yamashina side, there is a railroad signal (1st block signal, with 5 lights). When the aspect of the signal (the 1st home signal) in the Yamashina Station, which is located ahead the first block signal, is 'stop' (the red light is on), the aspect of the first block signal indicates 'speed restriction' (yellow + yellow) are lit). Then, the train running on the Kosei westbound track obviously slows down near the exit of the tunnel.

Nagara Tunnel on Nishi-Otsu Bypass (National Route 161)

The Nagara Tunnel is a 1,305 m-long road tunnel constructed along the Biwako nishi jukan road between Fujio Okumachi and Ojiyama ramps. It provisionally started service in 1980 with two lanes. The whole length of this tunnel, like that of Nagarayama (railroad) tunnel, is in Otsu City. Next to the exit of the Nagara Tunnel on the Nishi-Otsu side, there is another tunnel, the Yamagami Tunnel (131meters long).

As a part of the bypass's expansion project to four lanes, another tunnel has been under construction to the northwest (the mountain side) of the tunnels in service. This tunnel passed completely through to the other side as of the end of February 2008, and afterwards, operations including the pavement work have been on going.

The First Tunnel for the Lake Biwa Canal

The First Tunnel (Nagarayama Tunnel) for the Lake Biwa Canal, a tunnel constructed between Otsu City and Yamashina Ward in Kyoto City, has the total length of 2,436 meters, passing through Mt. Nagara.

The shaft (duct) is opened at two points, the first shaft (47 meters deep) is found at 1,695 m from the tunnel entrance on the Otsu side and the second shaft (20 meters deep) is located at 2,136 m from the entrance. The tunnel has a 1/3,000 downward gradient toward the direction of Kyoto.

With the construction of Nagarayama Tunnel (railway) on the Kosei Line (previously mentioned), some parts of the section were renovated and rerouted.
For further details, see 'Renovation of the Lake Biwa Cannel accompanied with the construction of the Kosei Line'

Nearby sightseeing spots

Onjo-ji Temple (commonly known as Mii-dera Temple, Sango (temple's title) is 'Nagara-san').

[Original Japanese]