Ui Sinseol Line train. Yonhap News Seoul City announced on the 14th that it will introduce a wireless communication-based train control system (CBTC) to relieve congestion on the Ui Sinseol Line. CBTC is a signaling system that controls the safety gap between trains using real-time train location information transmitted from the train through wireless communication. This allows trains to run at closer intervals. The existing track circuit method generates heat by flowing electrical signals along the track.