Sentence:  Sixty minutes divided by the <WSD>headway</WSD> gives a potential figure for 'trains per hour' - the simplest possible and most simplistic definition of capacity, termed line capacity. 
Meaning of the word marked with <WSD> tags:  The interval of time or distance between the fronts of two vehicles (e.g. buses) moving in succession in the same direction, especially along the same pre-determined route.