単線

1. Origins, structure, and basic meaning

• Structure: 単線 (たんせん) is a compound noun for a railway section having only one track for trains in both directions.
• Basic usage: 区間は単線だ predicates a track arrangement requiring trains to pass at stations, while 単線の線路が延びる modifies the one-track railway through mountains.

2. Common pitfalls and similar expressions

• Operating section and physical track
  • 単線なので行き違う concerns an operating constraint, while 単線の線路 concerns physical structure. The noun does not mean one electrical wire.