noun
planned railway line
Refers to a railway line that is in the planning stage, not yet constructed or in operation.
この計画線は2030年の開業を目指している。
This planned line is aiming to open in 2030.
未成線 refers to a line that was planned but never completed, often with a sense of abandonment, whereas 計画線 is still actively planned.
Compound of 計画 (plan) and 線 (line).