also: ブルートレーン
noun
blue train; sleeper express train
Refers to a long-distance night train with sleeping cars, originally named after the blue color of the carriages. Now largely historical as most have been retired.
かつてブルートレインは日本各地を結んでいた。
Blue trains once connected various parts of Japan.
ブルートレインの寝台券は予約が難しかった。
It was hard to reserve a sleeper ticket on the blue train.