SR 99 Alaskan Way Viaduct
Client: Washington State Department of Transportation (WSDOT)
Location: Seattle, Washington
Project Value: $3.3 Billion
Market: Underground & Tunneling / Transportation
Services: Quality Assurance Management, Tunnel Inspection
Key Features: 2-mile double-deck highway tunnel, world's largest TBM at the time of construction, advanced safety and ventilation systems
The SR 99 Alaskan Way Viaduct Replacement Tunnel is a landmark $3.3 billion transportation project that created a resilient, two-mile, double-deck highway tunnel beneath downtown Seattle for the Washington State Department of Transportation (WSDOT). Constructed using "Bertha," the world's largest tunnel boring machine at the time, the tunnel replaced the aging Alaskan Way Viaduct with a modern underground corridor designed to improve mobility, safety, and seismic resilience.
The tunnel features two travel lanes in each direction and incorporates advanced life safety systems, including ventilation, fire suppression, traffic monitoring, and emergency refuge areas throughout the facility. EPC Consultants provided quality assurance management and tunnel inspection services, helping ensure construction met the highest standards of quality, safety, and performance throughout this nationally recognized infrastructure project.