Editing Shinkansen (section)

=== Mini-Shinkansen ===
{{Nihongo|Mini-shinkansen|ミニ新幹線}} is the name given to the routes where former narrow-gauge lines have been converted to standard gauge to allow Shinkansen trains to travel to cities without the expense of constructing full Shinkansen standard lines.

Two mini-shinkansen routes have been constructed: the [[Yamagata Shinkansen]] and [[Akita Shinkansen]]. Shinkansen services to these lines traverse the [[Tohoku Shinkansen]] line from Tokyo before branching off to traditional main lines. On both the Yamagata/Shinjo and Akita lines, the narrow-gauge lines were regauged, resulting in the local services being operated by [[701-5000 series|standard-gauge versions]] of {{Track gauge|1,067mm}} suburban/interurban rolling stock. On the Akita line between Omagari and Akita, one of the two narrow-gauge lines was regauged, and a section of the remaining narrow-gauge line is dual gauge, providing opportunity for Shinkansen services to pass each other without stopping.

The maximum speed on these lines is {{convert|130|km/h|mph|abbr=on}}, however the overall travel time to/from Tokyo is improved due to the elimination of the need for passengers to change trains at [[Fukushima, Fukushima|Fukushima]] and [[Morioka, Iwate|Morioka]] respectively.

As the [[Loading gauge]] (size of the train that can travel on a line) was not altered when the rail gauge was widened, only Shinkansen trains specially built for these routes can travel on the lines. They are the E3 and E6 series trains.

Whilst no further Mini-shinkansen routes have been proposed, it remains an option for providing Shinkansen services to cities on the narrow-gauge network.{{Citation needed|date=May 2025}}

====Proposed Ou Base Tunnel====
Construction of a [[Base tunnel]] on the [[Yamagata Shinkansen]] is proposed, with JR East having undertaken a survey of a planned route from Niwasaka to Sekine, just south of Yonezawa station.<ref>{{Cite web |date=7 November 2022 |title=Yamagata mini-Shinkansen base tunnel proposal makes progress |url=https://www.railwaygazette.com/infrastructure/yamagata-mini-shinkansen-base-tunnel-proposal-makes-progress/62884.article |url-access=subscription |access-date=12 November 2022 |website=Railway Gazette International }}</ref> {{convert|23.1|km|mi|abbr=on}} of the proposed {{convert|24.9|km|mi|abbr=on}} line would be in tunnel, mostly to the north of the existing {{convert|88|km|mi|abbr=on}} Fukushima – Yamagata section. To be built on an improved alignment, the tunnel would lower journey times between Fukushima and Yamagata by ~10 min due to a proposed line speed of up to 200&nbsp;km/h.

The tunnel would avoid the Itaya Toge pass through the Ou mountains west of Fukushima. Gradients range from 3.0% to 3.8% and the line reaches an altitude of {{convert|548|m|ft|abbr=on}}. The curvature and steep grades limit train speeds to {{convert|55|km/h|mph|abbr=on}} or less, and the line is vulnerable to heavy rain and snowfall as well as high winds. Between 2011 and 2017 a total of 410 Yamagata mini-Shinkansen services were either suspended or delayed, and 40% of these incidents occurred on the line over the Itaya Toge pass.

If the {{Yen|150 billion}} base tunnel is authorised, detailed design would take five years and construction another 15 years. The cost could increase by {{Yen|12 billion}} if the tunnel were to be built with a cross-section large enough to permit the line to be upgraded to the full Shinkansen loading gauge.