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Traffic Engineering assigned this issue to Scott Brunner

This has been reported so many times and nothing is ever done about it. Not even one car can make that left onto Hightower before the turn signal turns yellow and you are left guessing as to when the light in the opposite direction will turn green. So frustrating and so dangerous.

The geometry of this signalized intersection currently only provides a single lane for both eastbound and westbound through traffic on Pine Grove Road. For westbound traffic approaching the intersection, left-turning motorists attempting to turn left onto southbound Hightower Road share the same single lane with through traffic -- left-turning vehicles do not have their own left-turn lane. Therefore, when the left-turn arrow is provided for this WB-to-SB left turn, the heavy opposing eastbound through traffic must be stopped for the duration of the left-turn arrow interval.

Since westbound left-turners do not have their own lane, they are randomly intermingled within the approaching shared westbound left/thru lane. The traffic signal has no way of knowing how many motorists actually want to turn left and how many want to go through from the single lane -- its a mathematically random occurrence. Sometimes left-turners can get a gap in the opposing EB traffic quickly and accomplish their left-turn, but sometimes they get delayed for some time. When one or more left-turners get stuck trying to make a left-turn, a queue starts to form behind them. The intersection has sensors along the WB shared left/thru lane that detect the length and duration (delay) of that building queue. When the queue reaches a certain length and delay, the sensors place a call to the controller to implement the WB-to-SB left turn arrow phase. The duration of the green arrow phase is determined based on the behavior of how the westbound queue dissipates, which again is influenced by the proportion of left-0turners and those just going straight through. Therefore, the left-turn arrow phase is intentionally not a fixed phase sequence within each signal cycle or of a pre-determined time duration -- it varies based on the traffic sensors interpretation of when left-turners are creating a delay, and the left-turn arrow can appear at the beginning, middle, or at the end of the regular east/west circular green phase when it is most needed. The heavy eastbound traffic cannot absorb implementing the westbound left-turn arrow phase each cycle for a significant amount of time, otherwise the EB queues would be twice as long as they are already, which is already excessive. The current control scheme attempts to provide the best balance of delay among the completing movements. This is not a new or unique operation as adaptive signal control sequencing, (which has continually varying phase sequencing) is becoming more prevalent in the United States. This is a very simple and limited example of that methodology. The minimum green, yellow interval and all-red-clearances are consistent or exceed normal signal control standards, so a reasonably prudent driver should not encounter a safety issue with the implemented operation. We have implemented this type of special phasing and algorithm at other similar situations throughout the city.

We will go ahead and revisit the operation now that school is back in session to see if any adjustments are warranted, but the current operation will generally remain as it is. We do appreciate the inquiry. If yo have any further questions, please feel free to contact us.

-Scott Brunner, City Traffic Engineer
sbrunner@roswellgov.com

I appreciate response, however none of the above takes into account the fact that westbound traffic is held at the intersection of Waterford Way and the current timing of the light turns yellow before the first car can travel the distance from Waterfor to begin the turn on Hightower it also does not address the fact that once you have pulled forward, you can no longer see the light at Waterford and the auxiliary light at the corner of Hightower and Pine Grove no longer illuminates on green, it is dark, so you are guessing as to what is going on, or have to look to your right to the signal that faces Hightower to figure out what is going on. This part is a new problem. It did not do this a few months ago.

Thank you for the clarification. The circular green LED will be replaced and we will check the sensitivity of the loops and make sure the programming is operating per design. We will keep this SCF item open until the situation is confirmed resolved.

The circular green indication was replaced, and the loop detectors and programming were checked and found to be working properly. We are going to perform some additional field observations during peak times to see if we can identify any phase changes or intervals operating differently than designed. We will keep this SCF open for a few more days.

Closed per S.Brunner