Terminology

All professions have technical jargon. Traffic engineering is no exception.

This post will be a running commentary with an attempt to define some of the technobabble that will be in this blog. I will attempt to keep it in some sort of order... Maybe grouped in some way, maybe alphabetical... No promises.

DEFINITIONS

MAX (Max1, Max2, Max3) - The max time is the maximum amount of time that the signal will serve a phase after an opposing call is served.  For example, if a signal has served the MIN green time and is resting green on the main street, and there is constant traffic on the main street, the MAX timer starts timing after the first conflicting movement has a valid vehicle call.  If the traffic on the main street reduces, and the signal gaps out before the MAX timer times down to zero, then the signal will gap out and serve the side street.  This is similar, but different than forcing off in coordinated mode.
MAX (Dynamic) - NTCIP controllers have a dynamic max ability.  This allows the controller to be set with a short max (20 or 30 seconds) for each movement, but also with a higher dynamic max time and a step interval.  Essentially, if the traffic is low volumes, the signal will gap out, and the normal MAX time will apply.  As the traffic volumes increase, some of the phases of the signal will begin maxing out, and the signal will increase each phase's MAX time by the step interval up to the Dynamic Max time.  As traffic volumes decrease, the Dynamic Max time will reduce automatically.  This means that the main street could have a 20 second MAX time, but a 70 second Dynamic Max Time with a 10 second step interval.  This allows the signal to breathe for the uncoordinated cycle time based on the past 2 to 10 minutes of actual use.
Overlap - an overlap is a special type of signal operation that is allowed to operate across one or more vehicle phases. There are a lot of uses for overlaps to be described later
Phase - a phase is a distinct movement at a signal. Generally, the through movements are each given a phase number that is even. Generally, the protected lefts are given a phase number that is odd.
Recall - in general, all of the recall types can be assigned to any or all of the vehicle phases. When a signal has one or more phases in some form of recall, the signal will cycle between the movements with the recalls. Many signals are programmed to have the signal rest on the main street by putting the main street thru movements in min recall.
Recall (max) - this is where the phase is constantly being serviced for the maximum amount of time, either MAX1, MAX2, MAX3, Dynamic Max, the coordinated operation split time, or for a coordinated phase, the currently available bonus time plus split division time.
Recall (min) - this is where the signal will serve the minimum green time programmed, plus the variable initial green time.
Recall (pedestrian) - where the signal automatically will serve the pedestrians each cycle. This may be for any, or all phases.
Recall (soft) - Soft recall is not used very often. Essentially, this mode of recall allows the signal to cycle to different movements when there are no active vehicle calls on the movements in soft recall. This can be useful for low volume operations, to allow the signal to cycle between some movements before going back to the main street. The signal needs to have good stop bar detection in order to make this work. Care needs to be taken to make sure that the signal can not create a yellow trap with the soft recall settings..