The Hakkōda Tunnel is part of the northern extension of the Tōhoku Shinkansen, and is located between the stations of Shichinohe-Towada and Shin Aomori. Preliminary work on the tunnel began in August 1998, with ground broken in June 1999. On its breakthrough on February 27, 2005, it surpassed the Iwate-Ichinohe Tunnel of the same Tōhoku Shinkansen to become the world's longest terrestrial (land-based) tunnel, but was surpassed only two months later by the Lötschberg Base Tunnel in Switzerland. However, the Lötschberg Base Tunnel has only a single track for most of its length, and therefore the Hakkōda Tunnel remains the longest double-tracked terrestrial railway tunnel in the world.