Northgate Link Extension

LOCATION:  Seattle, Washington   |   OWNER:  Central Puget Sound Regional Transit Authority
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The Northgate Link Extension Light Rail project will connect Sound Transit’s University Link light rail segment to the Northgate business/retail center in Seattle, Washington. The project will form part of a system connecting four major urban centers to the existing Central Link (which extends from downtown Seattle to SeaTac airport). It consists of 4.3 miles (6.9 km) of double-track light rail, 3.2 miles (5.2 km) of which will be in twin bored soft-ground tunnels, and 1.1 miles (1.7 km) of which will be in retained cut fills and elevated structures. Precast segments will be used for the tunnels.

The project also includes two underground transit stations (U District and Roosevelt), one elevated station (Northgate), a portal structure, and 20 cross passages. Both underground stations have been designed as bottom-up excavations, and the cross passages are anticipated to be sequential excavation method structures. The project takes place in an area characterized by dense, urban neighborhoods and complex subsurface and groundwater conditions, which will require optimizing the location and alignment of the underground elements.

McMillen Jacobs Associates is the prime consultant. We are providing project management, tunnel and underground structure design, estimating and scheduling, and geotech­nical engineering services on a team that combines the talent of more than 30 firms, including key teaming partners Parsons Brinckerhoff, KPFF Consulting Engineers, Hewitt Architects, and LMN Architects. The team is producing final design contract document packages for 10 construction contracts.

With a target completion date of 2021, the Northgate Link Extension aims to increase light rail ridership, improve travel time, and add transit capacity to the congested Interstate-5 corridor.