Sentence:  The accident led to the introduction of <WSD>TETS</WSD>, or Trains Entering Terminal Stations (London Underground) or alternatively Moorgate Control (National Rail), named after the disaster and introduced on all dead-end terminal stations. 
Meaning of the word marked with <WSD> tags:  (initialism) Trains Entering Terminal Stations: a failsafe device for stopping trains that are entering a station at the end of a railway line.