 Manual systems of working trains are common in area with low numbers of train movements (such as 1 per day), and headways are more often discussed in the context of non-manual systems.Automatic block signalling is probably the most relevant to the calculation of headways.For automatic block signalling (ABS), the headway is measured in minutes, and calculated from the time from the passage of a train to when the signalling system returns to full clear (proceed).