複線

1. Origins, structure, and basic meaning

• Structure: Written 複線 and read ふくせん, it denotes a railway section with two parallel tracks, typically one for each direction.
• Basic usage: It is used for upgrading a single-track segment and increasing train capacity.

2. Common pitfalls and similar expressions

• Not two separate routes
  • It describes paired tracks on the same corridor, not unrelated railway lines.