It’s been a long time since TRANSYT first introduced signal “phases” in addition to “stages” – Introduced way back in TRANSYT 13 in fact. This simplified the specifying of signal arrangements considerably. However, there is one aspect of TRANSYT that is often overlooked – the specification of a second phase that controls a traffic stream or link. Part of the reason may lie with the User Guide, which hardly mentioned this facility – this will change however in future issues.
A second phase can be added via the “Signals” tab of the Traffic Stream Data screen, by selecting the “Phase2” option and referencing the second (associated) phase. Although the TRANSYT model only makes use of the second green time within the model and otherwise does not explicitly know what is being modelled, the specifying of a second phase is still useful when you wish to explicitly indicate to others that you are modelling, say, a left-turn filter situation. The green time of the traffic stream or link will be the combined green time of both phases. It isn’t actually necessary to model a filter in this way, as you could simply redefine a single phase to run over the same length of time as the two separate phases but this is more of a ‘modelling-only’ solution as the phasing arrangement would then differ significantly from that found within the controller.
N.B. When using a second phase to model a filter, the filter phase would be set up in TRANSYT to run till the end of the associated phase (although in reality the left turn arrow would be extinguished as soon as the main green started).
Finally, assuming the “phase” type has been set to “filter” then the file preference “Use phase colours in timing diagram” will allow you to more-easily see the presence of the filter in the timing diagram.