Arterial coordination optimization results in sets of offsets and phase sequences for each intersection. That provide the widest green waves.

 

Usually, the choice is made between 4 phase sequences:

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• Lead/Lead,

• Lead/Lag,

• Lag/Lead, 

• Lag/Lag.
   

There is, though, a special case when this set expands.

 

When the two opposite green through times and the red time add up to the cycle length, it is possible to service every intersection approach separately.

 

Such schemes are called Split Phasing, hereafter Splitting for brevity.

 

The most common case is that all movements of a particular approach are followed by all movements of the opposite approach.

 

This case is equivalent to Lead/Lag or Lag/Lead phase sequences, so the coordination solution may be obtained by employing the traditional software.

 

No traditional sequence can describe the second option, which we call Dividing. It involves dividing the red time into two parts. At that, all approaches can be served one by one, clockwise or counterclockwise.

 

These two schemes are equivalent if the red time is divided into equal parts.

 

Thus, Dividing adds 1 or 2 phase sequences to the traditional 4 ones.

 

At that, the optimization algorithm becomes more complicated, but the optimization sometimes results in wider green waves.

 

The Arterial Portraits and the Time-Space Diagrams below illustrate the case when Dividing in the 1st and 4th intersections improves coordination dramatically: the maximal possible sum bandwidth increases from 26 s to 51 s.