Plans for an expressway on the route were first drawn up around 1970, initially in the form of an elevated expressway over the Meguro River between Shibuya and Oimachi. The elevated expressway plan was shelved shortly thereafter, following concerns about environmental issues and local resident protests, but re-emerged in the 1990s in the form of a tunnel plan. The final plan for the southern portion of the tunnel, approved in 2004, followed Yamate Street and the Meguro River, in order to minimize tunneling under private property. Construction on the Yamate Tunnel began in 1992. The Takamatsu – Nishi Shinjuku segment opened on December 22, 2007. On the same date, an above-ground segment linking the tunnel to the Kumanochō Interchange in Itabashi and Toshima also opened. The section between Nishi Shinjuku and Ohashi opened on 28 March 2010. The last section linking Ohashi to the Bayshore Route opened on 7 March 2015.
Facilities
The tunnel has many operational and safety facilities. Among them are emergency telephones and cameras at 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 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 Route 3, required construction of stacked elliptical ramps in circumference and in diameter, similar in size to the National Stadium track. For soundproofing reasons, the junction was encased in over 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.
The Yamate Tunnel passes above the Yūrakuchō and Ōedosubway lines. It crosses below the Tōzai and Marunouchi subway lines, as well as the Keiō and Keiō New Lines and the Tōkyū Den-en-toshi Line. Additionally, the tunnel parallels the Ōedo Line along a segment between Nakai and Nishi Shinjuku Gochome Stations. Nakai and Nakano Sakaue Stations, lying beneath the Yamate Tunnel, have escalators that pass between Yamate's two tunnels.
