Add Traffic Signal Head Phasing Diagram to Reduce Connection Errors and to Improve Safety

Traffic signals are becoming more and more complicated nowadays. Traditionally traffic engineers will design the intersection based on traffic count data, field observation, and accident history and warrant analysis. Then drafters will draw the phasing diagram/construction/Traffic Signals for this intersection. Technologists will then implement timing plans and databases based on the drafts. Then the timing plan/database will be handed into signal installers. During all this process, if one chain is broken, then traffic signal safety and operation can be in hazardous situation. The proper application and design of the traffic signal is a key component in improving the safety and efficiency of the intersection. To remove all the uncertainness, a Traffic Signal Head Phasing Diagram will clarify unnecessary confusion.

Signal phasing is the sequence of individual signal phases or combinations of signal phases within a cycle that define the order in which various pedestrian and vehicular movements are assigned the right-of-way. While intersections are becoming more complicated, more functions/phases/movement are needed to adapt to different vehicle and pedestrian requirement, complicated phase sequences and signal head setup come along with it. Following are a few examples, including Dallas Left-Turn Display for Left-Turn Lead-Lag Signal Phasing, Diamond Interchange, Right-Turn vehicle phase overlap, pedestrian phases in a wide intersection that covers two consecutive vehicle phases. Traditional simple signal head design without clear designation may not work well for these complex situations. The solution is to draw a Traffic Signal Head Phasing Diagram/Notation.

The diagram can be drawn in existing traffic signal diagram, just by adding a few more signal head diagrams, with some notations on the side explaining the phase number or overlap number for that signal head. Or a table can be drawn to explain which color in Signal head is driven by which phase or overlap. It sounds like a simple improvement, but for large intersections this process will simplify the guessing process by installers, make engineer/drafter's job much clear, and also make the installers’ job much easier and reduce the risk of wrong connections.

The signal head phasing diagram can avoid unnecessary guesses from traffic professionals, provide a much clearer image of the operation of the controllers and traffic signal indications. One image is worth more than a thousand words!


Liu, Jiutang

Session title

#InnovativeTrafficControl (PS)


Traffic Operations & Management Standing Committee


Traffic Operations & Management