Today I found the word 寝台特急, which means a sleeper express train. I was surprised to see that it had furigana indicating that it should be read ブルートレイン or “blue train”.
Blue Train was the name given to sleeper trains that were popular in the 70s and often appeared in novels (I found it in a book written in 1980). Their exterior was blue, hence the name.
They stopped being used with the development of the Shinkansen and regional airports.
@Akira1108
I’m happy to hear that :) I’m not really familiar with trains either, but I like novels that take place in trains.