Lynnwood Link Extension

A 4.8-mile double-track extension of Sound Transit’s light rail system was delivered under a CM/GC contract, with Stacy Witbeck serving as the managing joint venture partner.  

The alignment runs through a narrow corridor parallel and adjacent to Interstate 5, requiring precise execution within limited right-of-way conditions. 

The route includes 1.9 miles of elevated guideway with direct fixation track and three miles of ballasted track in an at-grade guideway constructed within retained cuts and fills. 

The extension expanded Sound Transit’s light rail system while navigating a constrained transportation corridor and sensitive environmental conditions.  

Work 

The scope included construction of two stations, infrastructure for a future third station, and two large parking garages, along with extensive demolition, clearing and grubbing, utility relocations, and site work.  

Civil construction encompassed retaining walls, roadway improvements, and site enhancements surrounding the stations, as well as the civil components of systems installation and restoration work.  

To support construction within the constrained corridor, the team built a temporary trestle over a wetland using oscillating drill rigs and cofferdams and constructed a cast-in-place overpass supported by approximately 200 shafts measuring up to 20 feet in diameter and extending as deep as 80 feet. 

Stormwater management was a major component of the work. A temporary system was implemented during construction to collect and treat runoff across 55 acres of the alignment. The system included six basins, 157 Baker tanks, four ponds, 147 pumps, and 108 generators, processing an average of 850,000 gallons of water per month and treating a peak volume of nine million gallons in a single month. 

Impact 

Despite significant challenges, including unusually heavy rains, snow, wildfires, a local concrete strike, and the onset of the global pandemic at the start of construction, the project was completed on schedule.  

The team coordinated schedules to begin systems work prior to completion of construction, maintaining progress and minimizing delays. 

Collaboration 

The project required close coordination among joint venture partners and Sound Transit to navigate external disruptions and site constraints.  

Collaboration enabled flexible sequencing, overlapping construction and systems activities, and real-time problem-solving throughout delivery. 

Innovations 

• - Constructed a temporary stormwater management system during construction to collect and treat runoff from 55 acres along the alignment. 
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• - Installed six basins, 157 baker tanks, four ponds, 147 pumps, and 108 generators. 
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• - Processed an average of 850,000 gallons of water per month, with a peak month of 9 million gallons treated. 
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• - Implemented temporary trestle and wetland construction methods to support drilling and foundation work in constrained conditions.