Managing Traffic with updated Traffic Signals and Information Systems on Mercer Corridor

The Mercer Corridor Project is transforming Mercer Street into a principal arterial street that better serves the growing South Lake Union and Uptown urban centers while continuing to provide access to and from I-5 and the future SR 99 Tunnel for these neighborhoods and others to the north and west.  Given the volumes of traffic exiting and entering I-5 at Mercer Street and dispersing from Mercer to north and south streets, as well as west toward Queen Anne, Magnolia and Interbay, SDOT is installing new traffic signals and communications systems to move people and goods more efficiently along and across the corridor as efficiently as possible.  Enhancements to maximize the benefit of the new signals and communications are coming soon.

New Signal Light at Mercer Street and 5th Ave North

New Signal Light at Mercer Street and 5th Ave North

The Mercer Corridor project installed or updated 30 signals on Mercer, Valley, Roy, and Republican streets and on Fifth Ave N.  All of the signals are connected to SDOT’s Traffic Management Center to allow for better communication and coordination between signals.  Each signal includes a controller that can be equipped with new traffic control technology – adaptive signal control – which will be coming to the Mercer Corridor in the near future.  Adaptive signal control allows the signal system to be more responsive to real-time traffic conditions.  Detectors in the street will monitor traffic volumes and feed that information to signals downstream from the traffic flow, so they can adjust timing to better accommodate traffic flows.

New Signal Controller at Mercer Street and 5th Ave North

New Signal Controller at Mercer Street and 5th Ave North

Adaptive signal control is expected to be most effective during the periods before or after the peak demand periods in the corridor, sometimes referred to as “the shoulders.”  It will be less effective during the peak periods, especially the evening peak, when traffic is backed up trying to get onto I-5 and other destinations. Even the latest technology cannot move more traffic when there’s no space ahead.  Adaptive signal control is also expected to improve operations for people leaving Seattle Center after an evening performance or other event.  In that case, the signals would detect the surge of eastbound traffic, along with the lower demands on side streets late at night and give more green time to traffic on Mercer Street.

 

The Mercer Corridor will be the first application of adaptive signal control in the city.  The City Council provided $1 Million in SDOT’s budget to design and implement the system on Mercer.  Specification and design is starting in 2015, and the system will be implemented on Mercer in 2016.  The next phase of adaptive signal control, after Mercer, will be on Denny Way.

 

Mercer Corridor Aerial 10-14

Mercer Corridor Aerial 10-14

SDOT is also implementing other features on Mercer Street that will provide more information to those traveling on Mercer and to the engineers programming the signals.  The department is measuring travel times on Mercer using Bluetooth technology.  This new system collects and summarizes travel time information at multiple locations along the corridor so the engineers can zero in on specific problem areas or intersections.  The travel time information will be added to SDOT’s Traveler Information Map and on the Traveler’s app.  This and other information will also be displayed on new variable message signs at Ninth Ave N and Sixth Ave N along the corridor, as well as a new variable message sign that will be installed on Elliott Avenue W.

 

For up-to-minute construction updates join our project email list at: http://www.seattle.gov/transportation/mercercorridor.htm or call the 24-hour construction hotline at 206-419-5818.