Sentence:  At the same time the civil engineers knew that the older of the two Clyde bridges was in need of early renewal. The signalling engineers solved their problem by concluding that bi-directional working over all running lines on the later, wider bridge would allow the elimination of the <WSD>time-expired</WSD> structure. 
Meaning of the word marked with <WSD> tags:  (of a structure) At the end of its life.