Transit Priority Definition
- Transit SGs (Transit SGs)
- Coordination Priority (Coordination Priority)
- Free-Running Priority (Free-Running Priority)
- Transit Inputs (Transit Inputs)
Transit SGs
There are 8 Transit SGs available. The signal group numbers for transit priority are hard coded as SG 301-308. The signal groups are not necessary for transit priority to be used, but allow additional flexibility if you wish to have a separate signal head for the transit signal priority movement.
The Transit SGs will not be available within Vissim unless you select Use as VISSIM SG.
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These are the signal groups that must be timing for the transit priority to time. All signal groups flagged for this parameter must be timing before the transit priority can time. This is unlike overlaps that can time when any parent signal group times. Signal groups that conflict with parent signal groups will not begin timing until the transit priority has completed timing its clearance intervals. |
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This parameter defines the minimum green time that a Transit SG will serve before changing to amber. In the absence of any extension, the Transit SG will serve this minimum green time before it is eligible to te minate. The controller will enforce a minimum green time of 1.0 seconds if the value of this parameter is less than 1.0 seconds. The minimum green time can be abbreviated to the Start Green time of an active preempt. If any of the Parent SGs are flagged for Zero SG Green Time for an active preempt, the minimum green time will be aborted for the Transit SG. Values permitted are zero to 25.5 seconds. |
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| The time a Transit SG will time an amber indication before advancing to red. This time cannot be abbreviated by any operation. Values permitted are zero to 25.5 seconds. | |
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The time a Transit SG will time a red indication before any signal groups that conflict with its Parent SGs will be allowed to begin timing. Values permitted are zero to 25.5 seconds. |
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Defines the time that a Transit SG will extend its green interval following the dropped detection (either loss of presence on a Presence detector or Check Out on a Check In/Check Out detector). During this extension, the Transit SG will remain green unless Parent SGs are terminating before the extension expires. Values permitted are 0 to 255 seconds. |
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By default, transit priority requests with lower estimated travel times are served ahead of transit priority requests with higher estimated travel times. For higher priority transit movements, the priority should be defined to a higher value than that of lower priority transit movements. Transit movements with higher priority values (regardless of estimated travel time) will be served ahead of those with lower priority values. Values permitted are 0 to 255. |
If this option is selected, the corresponding signal group will be passed to Coordination Priority
- Coordination Transit SGs (Coordination Transit SGs)
- Coordination Vehicle SGs (Coordination Vehicle SGs)
Coordination Transit SGs
Coordination Vehicle SGs
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When a signal group that conflicts with a priority signal group is timing, the controller will abbreviate it in order to serve the Priority SGs faster. Normally, the controller will be allowed to shorten the conflicting signal group down to its Min Green time before terminating the signal group. Programming a non-zero value for this parameter will guarantee the longer of the signal group Min Green or Priority Minimum Green time before it will be terminated to serve a priority signal group. Values permitted are 0 to 255 seconds. |
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When computing the maximum duration for a priority extension, the controller will take into account the minimum timing for each signal group in the recovery cycle (the cycle following the priority extension). The controller can only extend the Priority SGs to the point where it can still serve the greater of the Min Green time or recovery minimum green time to all subsequent signal groups by the end of the next cycle.
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Priority Progression modifies how coordinated signal group splits are shortened during a priority request. Any coordinated signal group flagged for this parameter will guarantee a minimum green band from the computed start of signal group green. Without this parameter, coordinated signal groups can be terminated at the computed start of green provided they have been green for the priority minimum green. Flagging coordinated signal groups with this parameter improves vehicular progression, but limits how much the current cycle can be abbreviated in order to serve an early priority request in the next cycle. |
Free-Running Priority
Free-Running Transit SGs
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Defines the priority mode of the Transit SG. This parameter is only observed when the controller is operating in the Free-Running Mode. The modes are:
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Extend Limit is only observed when the controller is operating in the Free-Running Mode. When using a Free Priority Mode other than None, this is the maximum time that a Transit SG will be allowed to extend once the associated Transit SG changes green and the arrival timer counts down to zero. Note that the Transit SG may be passively extended if all Parent SGs still have enough time remaining beyond the priority extension limit. Values permitted are 0 to 255 seconds. |
Free-Running Vehicle SGs
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When a signal group that conflicts with a priority signal group is timing, the controller will abbreviate it in order to serve the priority signal group faster. Normally, the controller will be allowed to shorten the conflicting signal group down to its Min Green time before terminating the signal group. Programming a non-zero value for this parameter will guarantee the longer of the signal group Min Green or Priority Minimum Green time before it will be terminated to serve a priority signal group. Values permitted are 0 to 255 seconds. |
