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Cycle length optimization

It is well known that to coordinate traffic lights, the cycle length C must be the same (or proportional) at all intersections. Сhoosing the proper C value is not trivial. The greater cycle length does not always mean a wider green wave. On the contrary, it can narrow it. The wrong choice can significantly worsen the road throughput.

Green Traffic Software helps traffic engineers/traffic management systems avoid such troubles. For any urban arterial, it shows how the green wave responds to changes in C. It presents the 3-criterion plot that shows the maximum possible sum bandwidth, efficiency, and attainability as functions of the cycle length over the interval of its values chosen by the user.
 

Bandwidth is the number of seconds during which vehicles traveling at the given speed can move through the entire arterial without stops. The sum bandwidth is the sum of two opposite bandwidths.
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Attainability is the ratio of the arterial bandwidth to the shortest green through time on the arterial, measured in %%. Obviously, the bandwidth cannot be greater than the shortest green time, hence the maximum possible attainability is 100%*).

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Efficiency is the ratio of the bandwidth to the cycle length. Upper limits for poor, fair, and good efficiency are 0.12, 0.24, and 0.36, respectively. Values above 0.36 are considered great efficiency.

  1. Fill in the input table:

    • Define the intersections, noting that each can have a different cycle length.

    • Set the cycle length interval you’re interested in analyzing.
       

  2. Press the Choose button:

    • Green Traffic Software calculates the optimal cycle length within the specified interval, providing the maximum sum bandwidth, attainability, and efficiency for each cycle length (C) in that range.
       

  3. Select the desired cycle length (C):

    • Once selected, the green and red times in the table adjust proportionally to the chosen cycle length.

    • The Arterial Portrait is generated instantly, visualizing the coordination.
       

  4. Click any dark asterisk:

    • Access all necessary coordination details, including the Time-Space Diagram, offsets, and phase sequences.
       

No traffic volumes, saturation flow rates, or capacities are required.

Input table
3-criteria graph
Arterial Portrait
Time-Space Diagram, Outbound direction is prioritized

Morning peak hour (Out: 37 s, In: 21 s)

Time-Space Diagram, traffic flows are equal

Approximately equal traffic flows

(Out: 29 s, In: 29 s)

Time-Space Diagram, Inbound direction is prioritized

Evening peak hour (Out: 22 s, In: 36 s)

Optimizing the cycle length is critical for balancing efficiency and bandwidth. For instance, in this example:

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  • Reducing the cycle length (C) by just 3 seconds, from 121 s to 118 s, decreases the sum bandwidth by nearly 20% (from 58 s to 47 s).

  • Refer to the 3-criteria graph for a visual representation of this impact.
     

Green Traffic Software makes cycle length optimization simple, intuitive, and highly effective for achieving your traffic coordination goals.

* For details, see the Traffic Signal Timing Manual by US Federal Highway Administration.

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