Big yellow train
 

They retired the track inspection train
And put it in a train museum
...
https://www3.nhk.or.jp/nhkworld/en/n...0around%202027.

https://cimg4.ibsrv.net/gimg/www.fly...2043bffd08.jpg

Coming from depot in Shinagawa heading towards Tokyo Station.

Dr. Yellow!

How will they inspect the Shinkansen tracks going forward?

Instruments have improved and involved over the years that now all instruments for the inspections are compact and small enough that can be installed on regular revenue passenger trains. Now one shinkansen train will be fitted with the Instruments and inspections will be done during regular scheduled Shinkansen run.

The example of how Instruments have evolved, one of the Instruments I use as a chemist is Mass Spectroscopy and when I was in a graduate school this Instrument occupied the entire room of the size of a large conference room. Now Mass Spectroscopy is the size of desktop computer and is far faster and far more advanced in analysis then when I was in a graduate school.

P.S.
There are two yellow inspection trains called "Dr. Yellow." This inspection cars are officially called Shinkansen Denki-kidou Sougou-Shikensha 923 (Shinkansen Series 923 train, 新幹線電気軌道総合試験車923形). One is called T4 Configuration which belongs to JR Tokai, and another almost identical one (also yellow in color) is called T5 Configuration which belongs to JR West.

The one which has retired this January is T4 Configuration which belongs to JR Tokai. T5 Configuration which belongs to JR West will continue to run least till 2027. You can still be possible to see "Dr. Yellow" running on a track. JR West has not said the exact retirement date of T5 Configuration, JR West has said possible to run T5 Configuration beyond 2027. Also, JR West said they have not finalized the inspection plan after the retirement of T5 Configuration.

JR East has an inspection car called E936 Series (nicknamed East-i) which runs on Tohoku and Jyoetsu Shinkansen. It is not yellow in color, and nobody seems to give a damn about E936 where "Dr. Yellow" enjoys celebrity status.

JR East E936

Spotted it at JR Kyoto Station in March 2023. Glad I got to see it before it was retired.

https://cimg1.ibsrv.net/gimg/www.fly...a246eb1f5.jpeg
https://cimg2.ibsrv.net/gimg/www.fly...d5a04d5b3.jpeg

Becusee it is too normal looking, paint it a striking/stand-out colour and it would rise in fame.

https://cimg4.ibsrv.net/gimg/www.fly...8a61905e48.jpg
(picture from the Internet, not mine. I just learned about this one today)

Wow, really great photos on this thread!

JR Tokai will fit four N700S regular passenger trains with instruments to do Shinkansen track inspections. These trains will be called "Dr. S," and there will be a Dr. S logo next to the outside of the furthest entrance door (next to the engineer's control room) on Car 1 and Car 16. Dr. S logo will be added to odd number cars N700 Supreme logo on the outside of the car.

It is unlikely that JR Tokai will announce when and where Dr. S train will run. However, often there will be information leaked from the inside. This is not just JR Tokai, but pretty much all rail companies in Japan, when there is some unusual train running which will not be announced to the public, often information leaks from some insider in the company, and Tetsudou Otaku finds out about it beforehand. Same as one Dr. Yellow train left at JR West, schedule of Dr. Yellow run is not announced but Tetsudou Otaku often find out about it beforehand.

Announcement: Dr. S (in Japanese)

Here is some more information on Dr. S.
https://www.newsonjapan.com/article/148950.php

For anyone interested, NHK World's Lunch ON! program did a feature with the operator of Dr Yellow T4, on the last run of the train. It starts around the 18 minute mark. Sadly, it was also the final episode of Lunch ON!