A via button selects a specific route between a pair of signals where there is more than one way of getting from the entrance signal to the exit signal. This is indicated as a solid blue roundel where the via button acts in both directions, or as a blue triangle if the button only applies in one direction. Generally the method is to click the entrance signal, then the via button, then the exit signal. In some cases the use of a button is mandatory, in others where there is a preferred route the Via button is optional to select an alternative.
Last edited by GeoffM on 15/09/2016 at 03:00