JR East's Yamagata Shinkansen operates between Tokyo and a terminus at Shinjō in Yamagata Prefecture using the Tohoku Shinkansen tracks as far as Fukushima and the Ōu Main Line for the segment from there to Shinjō. Since the Shinkansen operates on the same tracks as regular rail services, it is often labelled a "mini-shinkansen".
Tsubasa services began in 1992, initially running to Yamagata with services extended to Shinjo in 1999. Between Tokyo and Fukushima, services are coupled to Tōhoku Shinkansen Yamabiko trains. From Fukushima, the trains run on their own at speeds limited to130 km/h with the fastest services between Tokyo and Yamagata taking just under two and a half hours.
Stations (from Fukushima): Yonezawa; Takahata; Akayu; Kaminoyama-Onsen; Yamagata; Tendō; Sakurambo-Higashine; Murayama; Ōishida; Shinjō
Route details and maps: http://www.jreast.co.jp/e/routemaps/yamagatashinkansen.html