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In|Sync’s Dynamic Period Explained

In|Sync 1.6 introduced many improvements that expanded features that were already established in In|Sync 1.4. Dynamic period is one of those features that has been an integral part of In|Sync’s method for proactively serving demand during changing traffic patterns. With In|Sync 1.6, we’ve incorporated feedback regarding In|Sync 1.4’s dynamic period and built an improved solution that responds to changing traffic conditions in a more effective manner.

In|Sync uses dynamic periods to determine when, how and how much a period can change, ensuring that In|Sync can constantly adjust to shifting traffic patterns. It requires that two conditions exist:

  • All intersections have the same period
  • All intersections in a configuration belong in a coordination group

Once these conditions are met, you can enable the dynamic period feature, define limits on how much a period can change and specify a reference intersection where global offsets can be applied. In|Sync then determines whether a change in period is necessary, the type of change and the amount of change by using a three-step approach.

Step 1 – Each Intersection Evaluates Miscellaneous Time Left in the Previous Two Periods

In|Sync Processors at each intersection evaluate how much miscellaneous time occurred in the previous two periods at the intersection. Miscellaneous time is excess time remaining at the end of the period after all demand for all phases has been served at least once.

  • If an intersection reports that the previous two periods did not have any available time, the intersection initially votes to increase the period.
  • If the previous two periods reported more than 20 seconds of available miscellaneous time, the intersection initially votes to decrease the period.
  • Otherwise, the intersection initially votes to keep the existing period.

 Step 2 – Each Intersection Compares Maximum Average Vehicle Density Against the Previous Time Period

The In|Sync Processor at each intersection then goes further and does the following analysis based on the maximum average vehicle density over the previous time period (dynamic period occupancy):

  • If the initial vote is to increase period length and:
    • Dynamic Period Occupancy is 5% or less, the vote is changed to decrease the period.
    • Dynamic Period Occupancy is greater than 5% and less than 20%, the vote is changed to keep the existing period.
    • Otherwise, the vote remains to increase the period.
  • If the initial vote is to keep the existing period length and:
    • Dynamic Period Occupancy is less than 20%, the vote is changed to decrease the period.
    • Dynamic Period Occupancy is between 20 – 50%, the vote remains to keep the existing period.
    • Otherwise, the vote is changed to increase the period.
  • If the initial vote is to decrease the period length, the vote is to decrease the period.

Step 3 – Collect Votes From Intersections and Determine Period Change

When dynamic period is enabled, In|Sync designates one intersection within the tunnel to be the decision maker regarding dynamic period changes. This intersection’s In|Sync Processor receives the votes from each intersection and ultimately makes two decisions: the type of period change and how much it should change. This evaluation happens:

  • Once every 60 seconds
  • Only if all processors are online
  • Only if there is not a period change already proposed
  • After two full periods have elapsed since a period change

 Determine Period Change Type

The decision-making intersection changes the dynamic period based on the following criteria:

  • If all processors vote to decrease, then the outcome is to DECREASE
  • If some processors vote to decrease and some processors remain the same, then the outcome is to REMAIN THE SAME
  • If any processor votes to increase, then the outcome is to INCREASE

Determine Period Change Value

Only the decision-making intersection determines the new period value. This value is based upon the following criteria:

  • If the vote is increase and there has never been a dynamic period change, increase the period by ¼ from the current period.
  • If the vote is increase and the previous dynamic period change was an increase, increase the period by ½ from the current period.
  • If the vote is increase and the previous dynamic period was a decrease, increase the period length by ¼ from the current period.
  • If the vote is decrease and there has never been a dynamic period change, decrease the period by ¼ from the current period.
  • If the vote is decrease and the previous dynamic period change was a decrease, decrease the period by ½ from the current period.
  • If the vote is decrease and the previous dynamic period change was an increase, decrease the period by ¼ from the current period.

After determining the type of period change and how much it should change, the deciding intersection processor sends the new period length to each intersection in the tunnel, which is applied to the next period. This process is continual, meaning that when dynamic period is enabled, In|Sync applies this analysis every period, continually adapting the length of the period to best accommodate current traffic demand.