“Delayed Green Arrow”

Thanh -- November 25th, 2008

"Delayed Green Arrow Sign". Also notice the "camera" above the light pole used to detect vehicles stopped at the intersection.Have you driven recently on Port Republic Road, East Market Street, or Main Street, tried to make a left turn at a light and wondered “did that light just skip my turn?” Then found that the green arrow turns on when the other lights turned red again? You may have even noticed the new sign that reads: “Delayed Green Arrow.”

In Spring 2008, the City of Harrisonburg’s Public Works Department began a new Transportation Management Program which began to look at City traffic patterns a little differently than it did before. With the help of modeling software to better visualize how traffic flows respond to signal timings and two full time staff members dedicated to signal timing plans, traffic studies, and coordination between intersections, some changes have been occurring throughout the city’s transportation network.

For example, at select intersections, a “delayed green arrow” pattern has been implemented to improve coordination between intersections along a corridor (major street). By delaying the green arrow and not having it “automatically” turn on and as a result make traffic in the opposite direction wait longer, models show that a larger number of vehicles would experience significantly less delays (less time stopped at a signalized intersection) with this “plan.”

But what about the vehicle wanting to turn left? When there are “breaks” in oncoming traffic the left turning vehicle could make its turn with the “yield on green”, or should it find no breaks in traffic, the light will know that it has been waiting, and at the end of the permissive green (aka, the green ball), it will stop oncoming traffic with a red light and provide a green arrow. Regardless, the vehicle will have an opportunity to safely turn.  This form of left turn sequencing is also known as a “lagging left”.

The following intersections are currently using lagging left turns:

  • Port Republic Road @ Bluestone Drive
  • S. Main Street @ Bluestone Drive
  • S. Main Street @ Grace Street

During its first 6 months, the City’s Transportation Management Program has modeled and coordinated several major corridors, including (but not limited to):

  • Port Republic Road between Devon Lane and Bluestone Drive
  • S. Main Street between Port Republic Road and Cantrell Avenue
  • High Street between South Avenue and Gay Street
  • East Market Street between Burgess Road and Chestnut Ridge Drive
  • University Avenue between Evelyn Byrd Avenue and East Market Street
  • Reservoir Street between Neff Avenue and Evelyn Byrd Avenue

With each adjustment in the coordination plans, these corridors are continually monitored and may require additional tweaks in the future as traffic patterns and volumes change. Additional corridors will also be studied and put into coordination as appropriate.

One thing to take into consideration when driving a coordinated corridor is that you may wait a little longer on the side street than you used to, as the coordinated system is programmed to hold on green on the main drag in order to allow traffic to progress smoothly.  Just about every light in the City has the ability to detect the presence of your vehicle, which is done using the cameras you see on the signal poles.  During periods of heavy volume, coordinated corridors are often programmed to turn off this detection for the main drag (or coordinated corridor) to allow for vehicle progression to occur despite gaps in traffic that would otherwise cause the signal to change to green for the side street.

The City of Harrisonburg’s Traffic Engineering page is currently under development and staff hopes to have a primer on traffic signal coordination made available soon.

Thank you to Brad Reed, Traffic Analyst with Harrisonburg’s Public Works Department, for his assistance  with and contribution to this story. Disclaimer: Thanh is also employed by Harrisonburg’s Public Works Department as Public Works Planner.

19 Responses to ““Delayed Green Arrow””

  1. Kenny says:

    I always wondered whose idea was it to delay left turns. Good thing over all. The only down side is it makes me take sorta risky left turns.

  2. Scott Rogers says:

    This is fantastic — thanks for providing this level of detail Thanh (and Brad). It’s great to know of the intentionality with which the City addresses traffic flow!

  3. Renee says:

    Wow, this is neat getting an inside view into how the city does traffic rules. Glad to hear Harrisonburg is doing advanced modeling and trying to improve the traffic-light system. Thanks, Thanh!

  4. rachel says:

    Very interesting. Recently I’ve been wondering whether the timing is slightly off on some signals in town, or whether people are just becoming much more bold in running red lights. With increasing frequency, I’ve been noticing that there are still vehicles traveling through the intersection in the opposite direction when my light turns green.

    Perhaps I should start noting the location and time. Traffic lights DO malfunction sometimes. (Remember the school bus accident back in March…?)

  5. Dave Briggman says:

    Which makes one wonder why there are intersections such as the one in front of the Sheetz and Country Club and Vine where one is coming off market onto Vine to turn left into Sheetz.

    Next time you have that green (but no arrow), notice how the oncoming traffic doesn’t move because they have a red.

    What a great place to put an arrow where none has been placed.

  6. Dave — you make a great point — I’m never sure whether the oncoming traffic (from Hawkins Street) has a green light or not. I suppose both directions used to be green simultaneously, and now they alternate??

    Another (possibly) similar intersection is the traffic light leaving the Valley Mall onto University Boulevard, between Evelyn Byrd and East Market. I believe both directions used to be green simultaneously, and now they alternate, but it almost seems like there should be a green arrow, or a “you don’t need to yield to oncoming traffic on green anymore” sign.

  7. Dave Briggman says:

    Which still doesn’t explain why the timing of the City traffic lights on South Main from Cantrell and East Market from Vine still, consistently, stop you at each light.

  8. Christa says:

    Hey Dave, it just gives you more time to talk on Candid Comment at a standstill, instead of driving while talking. ;)

  9. Jack Thyson says:

    Thanh and/or Brad would certainly be more qualified to answer the light timing question but as it has been explained to me it is a question of the control systems that many of the intersections have. The newer systems such as the system at Vine/E Market/Country Club can handle a much more complex intersection because it can send any number of signals that allow for complex coordination. The older systems along E Market can basically send a timing signal that can easily get crossed up by any number of things such as a car sensor activating an out of sequence red light. Basically we have a lot of old control systems and they are expensive to replace and virtually impossible to reliably coordinate.

  10. Renee says:

    I was just at that light at Sheetz/Vine tonight going East on 33. What bugs me most about it is that if you get stopped and wait at that light, you will almost always also get stopped and have to wait again at Carlton St. (at the Texaco). That whole system of lights in that area is a good place for the city to look at next! :)

  11. I’m just excited at the prospect of having a second traffic circle at some point. Thanh — any idea when that will be? :)

  12. cook says:

    Can I mention my favorite traffic light issue here? When is the city going to restore the walk signals at E Market and Main St at Court Square? I sometimes feel like I am playing real-life-Frogger while carrying coffee.

  13. Renee says:

    cook – yeah, they’ve been covered up with black plastic for a while – i wonder what’s the hold-up in activating them?

  14. Thanh says:

    The lights downtown (traffic signals on Main St not being in coordination as they were before, and the pedestrian light at Court Square and 33 East being covered) are currently that way because of the downtown streetscape project. (Wires between the signals run underground and the ground was opened up for the sidewalk, etc work.) I do not know off hand when everything will return to “normal”.

    Scott, I’m glad, and I am confident to speak for my colleagues and say that, we’re glad you like the roundabout on Linda Lane! Current road projects in the works do not have plans for traffic circles/roundabouts (i.e. Erickson Avenue-Stone Spring Road, Port Republic Road, Reservoir Street, etc). However, there have been discussions of a possible roundabout on Mt Clinton Pike to service also Park Rd (EMU entrance) and Chicago Ave. That project along with future widening of Mt Clinton Pike between Virginia Avenue and west city limits has no timeline (until development in the surrounding area, including the County, occurs to warrant such need), and its not definitive that a roundabout would be there. There are also a few other private developments that show smaller roundabouts in their plans, so we may be seeing more soon.

  15. Scott Rogers says:

    Thanh —

    The roundabout likely only works for some traffic scenarios, so it’s not too surprising there aren’t any others currently in the works, but I am always impressed at how well it works over on Linda Lane.

    Thanks again for highlighting this work by the City to improve and refine traffic patterns. Without such information, I think it’s easy for some people to assume the City doesn’t care and isn’t doing anything.

  16. Brad says:

    I’ve been away for the holiday and am getting into this a bit late, but I have answers to many of everyone’s questions. Thanh had a great idea getting this article out so that you guys can learn more about how the city is growing its traffic program. As she mentioned, I hope to have a website out in the near future that will explain how a traffic signal functions and how we time and coordinate them. The site will also include a traffic signal comment form, which I strongly encourage everyone to use. I’ll keep everyone up to date on when we expect to unveil the site. We are currently aiming for January.

    rachel – Every signal in the city (and probably just about every signal in the country) utilizes a “conflict monitor”. These devices are hard-wired to prevent any conflicting movements from occurring and are tested regularly. If the monitor detects a conflict, the signal will go into flash mode until the problem is fixed. What you probably saw was just as you assumed, people running the red light. If you do suspect there is a problem with a signal though, please call Public Works at (540) 434-5928.

    Dave (Maket & Country Club/Vine/Sheetz) – We would love to put an arrow up for those turning into Sheetz, though we are currently unable to do so. To put it in a nutshell, each protected movement at an intersection is assigned a ‘phase’, be it a left turn, through movement, or right turn during which you have no conflicting traffic for your movement. An intersection can be programmed with a maximum of 8 of these. Keeping it simple, all 8 are currently in use at this intersection; therefore, a ninth, unavailable, phase would be needed to program a left turn arrow for that movement. We are currently looking into ways to reprogram the intersection to make it safer in general.

    Scott (Valley Mall & University) – As far as the arrow goes, if you are headed out of the bank/hotel lot or out of the mall, both sides do come up separately. I will look into what we can do to make the signal/signage clearer for everyone.

    Dave (coordination on S. Main St) – We are working hard to improve the coordination in this ‘corridor’, while also trying to prevent excessive side street delay. This is often a balancing act when coordinating a system of signals. We’ve experienced good ‘progression’ (traveling on Main St smoothly without full stops) during most of the day, but we hope to do much better and are working on an improved coordination plan.

    Dave/Renee (coordination on Market St) – Vine St through Cantrell Ave are wired to one another on a ‘system’, while University Ave through Chestnut Ridge Dr (including signals on University and Burgess) are wired together on another system. Carlton and Cantrell are currently coordinated with one another and we are looking into coordinating Vine with them as well (please see comment below). The University through Chestnut Ridge system was coordinated just the other week. If you are experiencing poor coordination within either of the two systems, please feel welcome to give us a call and I will be happy to see what is happening.

    Jack – Those responsible for coordination before our new Transportation Management team were unable to coordinate certain intersection, such as Vine/Market/Country Club, due to the complexity caused by the number of movements at the intersection and the fact that they did not have the resources to run a computer model to coordinate the intersection well. We are capable of coordinating Market St at the intersection of Market & Vine if we wish to do so, though we have been hesitant due to the amount of delay it will likely cause the already congested side streets. We are currently working on a coordination plan to accommodate everyone’s needs at the intersection, though have yet to find a model with which we are pleased. As for the “old control systems”, I’m not sure who told you that, but I’m glad they were incorrect!

    I’m excited to say that we will be finished with the new Traffic Engineering Division website in the near future. The site will go over the basics of how the city’s signals are timed and coordinated and will give everyone a look at the components used to operate a signalized intersection. We would love to hear everyone’s comments and suggestions, which is why the new site will also include a comment form dedicated to signal-related concerns. I encourage everyone to use the new form when it is released. In the meantime, if you would like to follow up or have any questions, please feel free to call the Public Works Department at (540) 434-5928.

  17. Renee says:

    Brad, thanks for the detailed responses! Interesting to know that the Vine St. area has maxed out with the number of phases that can be programmed.

    I think a web site to communicate with the public is a great idea! Getting around town is something that affects everyone, and I’m sure you will get a good response to it.

  18. Dave Briggman says:

    Thanks, Brad, for your comments…how cool is he?

    Thanh: How about feeding your stories to Miriam? ;-) Gee, I miss her on the radio — except when she ran block for City government.

  19. BANDIT says:

    Heard Dave B. got into a fender bender tonight at the inter section of Rt. 33 east and keezletown Rd….Hope everyone was OK and had a driver’s license.

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