In March 2022, a significant incident occurred while the Tohoku Shinkansen train "Hayabusa-Komachi 21" was traveling at approximately 60 km/h between Ueno and Omiya, where its coupler disconnected and triggered an automatic brake. The Transportation Safety Committee of Japan is investigating the causes behind this disconnection, revealing through a recent interim report that the mechanism ('teko') responsible for connecting and separating train cars was operating irregularly without commands. Following this, another similar incident was reported in September 2024 as the same type of trains experienced another unexpected disconnection, raising serious safety concerns regarding the operations of this rail service.

To understand the mechanics behind the coupler mechanism, the report indicated that the coupler lock is triggered by the 'teko' which is generally activated by commands from the driver's seat. However, in instances following the initial disconnection, both maintenance personnel and safety inspectors observed that the 'teko' was repeatedly operating without any commands being issued. This unusual behavior of the mechanism led investigators to explore if the steep 19.6-degree gradient at the incident site could have influenced the irregular operations.

JR East had released findings last December attributing the circumstances leading to these disconnections to electrical malfunctions in the coupler controlling device. As a preventive measure, the company announced plans to implement a system in all approximately 90 train sets that would ensure the coupler remains secured even if electrical output errors occur, showcasing their commitment to improving safety protocols in response to these troubling incidents.