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A deep dive on signal configurations. |
Signal Configurations
The Interval Model
You're probably familiar with phase, ring, and barrier model traffic signal timing, but did you know there are other models as well?
The interval model changes the signal through a series of steps called intervals. For example, the change from green to yellow to red requires three intervals, achieving what is typically done in one phase of the phase model.
The user sets up as many intervals as necessary to complete a whole cycle, thus breaking out of the phase model box to complete movements not otherwise possible.
The Benefit
High degree of flexibility and finer control at complex intersections.
The Limitation
May lack features common to the phase world, such as actuation and preemption.
Signal Configurations
Flashing Yellow Arrow
The flashing yellow arrow (FYA) is a signal that explicitly designates the permissive turn for protected/permissive and permissive-only movements.
Approved in the 2009 Manual on Uniform Traffic Control Devices (MUTCD), the FYA can help intersections run more efficiently by starting the permissive movement earlier than it would have been allowed in the absence of a flashing yellow arrow.
With FYA, the yellow trap is eliminated by separating the turning movement from its adjacent through movement; among other things, this allows for faster and safer service of preempts.
FYA is supported in modern local control software, like McCain's Omni eX� software.
Practical Application
Fort Meyers, FL
During peak periods, the left turn signal is displayed in protected-only mode. Then, during off-peak times, the FYA is used to provide a protected permissive display resulting in a smoother and safer flow of traffic.
And don't forget to register for, or watch on demand our Webinar Series on Signal Timing.
