The Yamate Tunnel carries the Central Circular Route (C2) of the Shuto Expressway in Tokyo, Japan, from the Takamatsu on-ramp in Toshima to near the Ōi Junction in Shinagawa. It has a length of 18.2 kilometers.
Lying 30 meters below the surface, about 70 percent of the tunnel was constructed by the tunneling shield method. The roadway consists of two lanes in each direction. Nearly all of the tunnel lies beneath Yamate Dori. On completion the Yamate Tunnel surpassed the Kan’etsu Tunnel on the Kan-Etsu Expressway, to become the longest road tunnel in Japan and the second-longest road tunnel in the world. Most of the tunnel follows the route of Yamate Street (Tokyo Metropolitan Route 317).
The tunnel has many operational and safety facilities. Among them are emergency telephones and cameras at 100-meter intervals. Fire-safety equipment includes infrared sensors, fire extinguishers, foam sprayers, and pushbutton alarms. Emergency exits leading to a separate emergency path are located no more than 350 meters apart. Stairways lead up to Yamate Street. A duct running parallel to the roadway supplies fresh air and removes exhaust. Dust-collection systems are designed to remove 80 percent of particulates from the air.
The Ohashi Junction in Meguro connecting the tunnel to the Shibuya Route required the construction of stacked elliptical ramps 400 meters in circumference and 175 meters in diameter, similar in size to the National Stadium track. For soundproofing reasons, the junction was encased in over 120,000 cubic meters of concrete. The structure was used as the centerpiece of an urban planning project that includes the Meguro Sky Garden park and several high-rise condominium towers.
According to wikipedia