Adaptive signal control reduces travel time in Seattle

Siemens SCOOT eases congestion and increases travel reliability on busy Mercer Corridor.

Siemens Mobility Adaptive Signal Control breaks Mercer congestion

For more than 40 years, Seattle’s Mercer Corridor was one of the city’s most significant transportation challenges.

It became even more of an issue when it circuitous one-way routes hindered access to Seattle’s fast-growing South Lake Union technology hub – home of Amazon’s headquarters, Google’s new campus, the Bill and Melinda Gates Foundation, the Paul Allen Institute for Brain Science, and major biotech campuses for the University of Washington. A major reconstruction that turned all Mercer Corridor streets into two-way routes unsnarled the traffic but didn’t resolve congestion issues.


To determine next steps, the Seattle Department of Transportation (SDOT) worked on a systems engineering process with the Transpo Group, a transportation planning and engineering firm. They identified an operator need for robust adaptive signal control (ASC) that could take advantage of existing equipment and integrate well with SDOT’s current and future traffic control systems. After an extensive industry survey of ASC offerings, SDOT selected Siemens SCOOT (short for Split Cycle Offset Optimization Technique). Because SCOOT’s algorithm adjusts signal timing in real-time to match traffic patterns, it has significantly reduced congestion on the Mercer Corridor since its deployment in 2017.

Documented success

SDOT also worked with the Transpo Group to develop internal and external performance measures, the latter giving the public valuable travel information. The measures were derived from vehicle detection equipment, including Sensys in-pavement sensors, EDI data aggregators, Acyclica Bluetooth/Wi-Fi readers, and transit agency data sources. Measurement of actual corridor performance validated the success of the SCOOT deployment in Seattle that continues today. Not only does SCOOT reduce congestion, it provides reliable travel times that drivers can count on to get where they’re going on time.


In short, SCOOT determines traffic levels, predicts the flow of traffic, and adjusts the amount of time available to each movement through an intersection. It uses detectors at every intersection to continuously measure traffic levels and update signal timing plans, optimizing them to minimize delays and stops. Timing changes are small enough to avoid major disruption to traffic flow and frequent enough to allow rapid response to changing traffic conditions. And, the solution is scalable so it can adapt to SDOT’s changing needs.