Intelligent Transportation System in line for refresher course

Illustration of Intelligent Transportation System. Image via Google images. Click to enlarge.

Sammamish’s new Intelligent Transportation System (ITS), intended to speed traffic along the main arterial, 228th Ave., through the City, has generated enough complaints that a refresh is likely, officials say.

The ITS is intended to synchronize traffic lights based on traffic demand through the entire corridor. The problem: left turn signals don’t “trip” as often as before, sometimes leading to three full traffic light cycles before left turns are permitted, according to some City Council Members at a recent Council meeting.

Complaints appearing on social media point to longer cross street red lights, even when there is little or no traffic on 228th.

On other occasions, cross streets have the green even when there has been no traffic.

City transportation officials are well aware of the problems.

In a response to complaints, Steven Chen, the traffic engineer of the City transportation department posted this on Facebook (posted by Gary Wilson from an email he received):

As you noticed the recent changes in traffic signal operations on 228th Ave, we just implemented an Intelligent Transportation System (ITS) Project on 228th corridor with installation of new Adoptive Signal Control Technology (ASCT) systems for 11 signals on 228th from Issaquah Pine Lake Rd to NE 12th Pl. The ASCT system is a form of traffic signal operation in which signal timing parameters are modified in response to real time changes in the traffic conditions in order to improve and optimize objective functions. It refers to technologies that capture current traffic demand data to adjust traffic signal timing to optimize traffic flow in coordinated traffic signal systems. More information on ASCT can be viewed on USDOT FHWA link…/everydaycounts/edc-1/asct.cfm.

The 228th ITS project turned on the ASCT systems during the week Oct. 5th. We are continuing to monitor the new ASCT system and work on fine turning the system over time. During the time while ASCT system is first turned on and being tested, it is expected that drivers may notice longer wait at side streets and left turns at some intersections. However, once traffic gets onto 228th from side streets, the overall travel time on 228th corridor should be reduced with the adoptive signal system. If you have comments or feedbacks based on your experiences at specific signal on 228th, please let me know. It will help us on fine turning the ITS system with additional programming as needed.

The traffic cameras on 228th are for intersection signal control and operation. The cameras are used for traffic video detection to program timing and operate the ITS system.

John Cunningham, the director of public works, told the City Council this week that staff is still working to fine tune the system. Under consideration: peak-off peak adjustments to the programming; yellow-arrow left turn capability, which has been adopted in Issaquah and Bellevue at certain locations; and other adjustments.

Council Member Tom Odell previously said there should be a multi-jurisdictional effort to install ITS on SR 202 from Sahalee Way into Redmond, especially at the East Lake Sammamish Parkway intersection, where there are long back-ups during rush hour. The northbound ELSP green onto and through SR202 lasts only 45 seconds, sharply reducing the through-put and increasing the backup on northbound ELSP.

Odell raised the need for ITS on SR 202 in connection with potential road widening of Sahalee Way (design and decision now put off to next year).

Cunningham added the following detail to how ITS is supposed to work:

The system is using what is called Adaptive Signal Control Technology (ASCT).  ACTS is a form of traffic signal operation in which the signal timing parameters are modified by the system in response to real time changes in traffic conditions (most notably traffic volumes and direction) in order to improve and optimize the signal systems operations.  Part of the way the system does this is to look at the real time input being received from both an individual intersection and from the dominant corridor (in this case 228th Avenue) and then adjust the signal timing within the parameters programmed in by the city.  The system has the ability to choose different signal timing patterns based on time of day, traffic volumes, day of the week, etc. based on real time data.

The system was turned on October 6th.  During the first few days of operation, the system supplier was in town to train city staff on how to operate/program  the system and King County signal maintenance staff on how to maintain the system.  The system supplier also did some fine tuning of the system while they were here.  When the system first went live, it was programmed using historical traffic count data supplemented with traffic count data collected during the month before the system went live.  One of the beauties of the system is that it records traffic count data on a continuous basis for all movements in an intersection.  Over the past month, the system has been collecting real time 24 hour/day traffic information and we have been observing the system in operation as well as have been receiving reports back from drivers using the system on its operations.  We are now starting the process of using the collected information to optimize the operation of the system.

The main goal of the system is to make the commute along the 228th corridor as efficient as possible.  The initial programming of the system was done with this goal in mind.  It is obvious from the feedback we have been receiving and from the observations we have made of the system during the past month that the initial programming has favored the 228th traffic at the expense of the side street and left turning traffic.  The trick now is to reprogram the system parameters so that the system provides an efficient, relatively delay free 228th corridor trip for this major traffic flow while at the same time not delaying the more minor side street and left turn traffic too much.

2 thoughts on “Intelligent Transportation System in line for refresher course

  1. Pingback: Looking ahead to 2016 in Sammamish | Sammamish Comment

  2. Pingback: Two years later, Sammamish fixing 228th stop lights | Sammamish Comment

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