McCain: Signal Timing and Coordination

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Greetings!

Traffic Signals Part II. Last month we began a two-part series on traffic signals. In our newsletter, The History of the Traffic Signal - Abridged, you learned how the traffic signal got its start, the evolution of signal timing, and the inception of adaptive signal control.

This month, we dive a little deeper, looking at the interval model, lane control, and flashing yellow arrow, along with their practical applications.

Signal Configurations: The Interval Model	Lane Control Software, Program 247	Signal Configurations: Flashing Yellow Arrow
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. Learn More McCain Webinar Series McCain offers free, educational webinars on hot industry topics like signal timing. Check out what's coming up!	Day-to-day signal timing can be fairly straightforward, but what about special events or incidents? Specialized software, like McCain's Program 247 lane control software, is designed for this very purpose. Lane control software is used to adjust traffic flow and lane configuration by time-of-day or in response to events and incidents. The software has fail safe modes, so that non-communicating traffic controllers do not display lane control signal indications that conflict with surrounding signals. It also allows the opening and closing of lanes to be rolled out in stages, such that lanes close with the flow of traffic, and reopen in the reverse direction. McCain's software allows for custom transitions for each possible lane pattern transition sequence: with 12 patterns that's 132 combinations! Practical Application Charlotte, NC North Carolina DOT uses a lane control system with 12 traffic patterns to close lanes during NASCAR races, converting traffic lanes to impromptu sidewalks. On normal weekdays, lanes are reversed to benefit morning and evening traffic flows.	The flashing yellow arrow (FYA) is a relatively new 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 Fort Meyers uses the FYA to battle peak and off-peak periods for intersections near schools. 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.

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