Sound Transit Northgate Link Extension

Sound Transit’s Northgate Link Extension Passenger Stations are now substantially complete. The 4.3 mile stretch of primarily underground track, includes 3 stations: two below-ground at University District and Roosevelt, and the Northgate elevated station. Service is scheduled to begin September 2021.

Greenbusch is the Acoustical and Vertical Transportation Consultant for the stations as a subconsultant to McMillen Jacobs working with Hewitt Architects and LMN Architects.

Greenbusch also performed Audio/Video Engineering as a subconsultant to LTK Engineering Services for the audio system following the requirements of NFPA72, to ensure intelligibility of the public address (PA) systems and is also responsible for audibility of emergency paging and alarms.

The firm also provided Construction Noise & Vibration Monitoring throughout the project as a subconsultant to multiple firms including O'Neill Service Group and Absher Construction. Vibration consulting services was provided for the specialized floating slab system that is an element of the track through the tunnel (N180) for Stacy & Witbeck Construction. The N180 Floating Slab Testing (Northgate Link-UW Station Tunnel) involved Frequency Response Testing (FRT) of the contractor-installed floating slabs to ensure the system is performing as predicted. GBG developed both a Calibration Test Plan and a Production Test Plan for the floating slabs that were designed for vibration mitigation.