Doctor Yellow (ドクターイエロー) is the nickname for a series of high-speed diagnostic trains that are used on JR Central's Tokaido Shinkansen and JR West's San'yō Shinkansen lines. The trains have special equipment on board to monitor the condition of the track and overhead wires, including special instrumented bogies and observation blisters. Line inspection is carried out at full speed, up to 270 km/h on the Tōkaidō Shinkansen. Doctor Yellow trains make three round trips between Tokyo and Hakata Station every month. Depending on the day, trains follow the stopping pattern of either Nozomi or Kodama trains. A similar type of diagnostic train called East i is operated by JR East on the Tōhoku Shinkansen. "Doctor" in the name "Doctor Yellow" refers to their test and diagnostic function, and "Yellow" refers to the bright yellow livery they are painted in. The original color scheme of yellow with a blue stripe (applied to the Class 921 track-recording cars) was created by reversing the colors (blue with yellow stripe) used by track-recording cars on Japan's narrow-gauge railways. Some Doctor Yellow sets are painted with a green waistline stripe rather than a blue one. In build and appearance, they resemble the production, passenger-carrying Shinkansen trains they are based on. Because the schedule for this train is not made public, witnessing a Doctor Yellow in operation is a matter of chance. As a result, seeing one is said to bring the witness good luck or happiness. Railfans have set up websites and social media accounts to predict Doctor Yellow's arrival dates and times at stations along the route. On 13 June 2024, JR Central announced that they would terminate use of Doctor Yellow trains on the Tōkaidō Shinkansen line in January 2025, with plans for farewell events – including commemorative train rides, displays, and souvenirs – to be announced at a later date. At the same time, JR West announced plans to retire their trains after 2027. They are scheduled to be replaced with commercial N700S Series Shinkansen trains that incorporate inspection and observation equipment.

List of Doctor Yellow trains past and present

For Tōkaidō and Sanyō Shinkansen

For Tōhoku, Jōetsu, Hokuriku, Yamagata, and Akita Shinkansen

Interior (Class 923)

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Preserved examples