Definition of "branch line"

branch line

noun
plural branch lines
1. (rail transport) A secondary railroad route or one subsidiary to a railroad's mainlines.
  Quotations
  But the states were generally concerned with the location of trunk lines and left it to cities and counties to worry about branch lines.
  1987, William H. Rehnquist, The Supreme Court
2. (rail transport) A non-through line which joins a mainline (or another branch or secondary line) and ends at a terminus.
  Quotations
  They saddled themselves with the handling of light flows on a multiplicity of branch lines, and they sacrificed the speed, reliability and low cost of through train operation, even over the main arteries of the system.
  1962 December, “Dr. Beeching previews the plan for British Railways”, in Modern Railways, page 377
  Above all, Eurostar needs to be proactive in improving the service, reducing fares, and getting back to a post-COVID normal, despite Brexit. Or is it that SNCF just feels London is on a branch line from the rest of Europe, and not worth bothering about?
  2023 February 8, Christian Wolmar, “Pressing issues to help Eurostar fulfil its ambitions”, in RAIL, number 976, page 39