This month, Japan begins saying goodbye to the famous "Doctor Yellow" special bullet trains that have diagnosed faults on the country's high-speed shinkansen lines in some form for around 60 years since the first generation.

The trains have developed a mythical status among Japan's rail enthusiasts as their operating timetables are not disclosed to the public. Their elusiveness has given birth to claims that those who spot them will be blessed with happiness.

The two Doctor Yellow trains, T4 and T5 editions, have respectively traveled along the Tokaido and Sanyo shinkansen lines spanning Tokyo to Hakata Station in the southwestern city of Fukuoka without passengers. Operations by the T4 will cease later this month, while the T5 is set to retire after 2027, according to their operators.

JR Central, which owns the T4, said in June it is retiring the aging train, which started operations in 2001, with no plans for a successor. Instead, passenger-carrying N700S bullet trains will be outfitted from 2027 with testing and observation equipment that can fulfill the role of checking tracks and overhead wires.

The T5, which belongs to JR West, made its debut in 2005.

As a testament to the yellow trains' popularity, an event in October at JR Central's Hamamatsu factory offered visitors a chance to tour inside one of them as part of celebrations to mark 60 years of Japan's shinkansen bullet trains.

Sales of Doctor Yellow-themed toys and other merchandise also spiked ninefold in the week after the retirement was announced.

According to JR Central, the first-generation Doctor Yellow, or the T1, came about shortly after shinkansen service began in 1964, amid concerns diagnostic measures were needed to monitor the strain on equipment from trains traveling at speeds of up to 210 kilometers per hour.

A 0-series shinkansen train was outfitted for the task and painted yellow, in a move believed to have been taken to ensure the train could be more easily spotted during nighttime work.

As daytime operations increased and with them chances of sightings, the names "Doctor Yellow" and "train doctor" entered the public lexicon.

Technology on the current T4 and T5 trains has advanced far enough that the Doctor Yellow bullet trains can run at a top speed of 270 kph while scanning for rail deformities measuring just millimeters.

Each conducts inspections in a round trip between Tokyo and Hakata, which are more than 1,000 km apart, over two days. The tests are carried out about once every 10 days.

"All I can express is thanks for the trains' long service," said Hiroya Mochizuka, an official at JR Central. On their disappearance, he said with a laugh that he hopes passengers imagine they may have "become doctors who ride the trains and carry on their diagnostic work."