In action Thursday afternoon, Sound Transit’s board of directors selected HDR Engineering Inc. to provide final design services for expansion of Tacoma Link light rail corridors and an expanded maintenance facility.

With nearly 10,000 employees in more than 225 locations around the world, the firm will bring its engineering, architecture, environmental and construction services team to Tacoma’s Hilltop neighborhood.

The light rail service will grow by 2.4 miles, connecting the Stadium and Hilltop districts to existing tracks that go through downtown Tacoma from Theater District to Tacoma Dome station.

Voters in 2008 approved a funding partnership to expand Tacoma Link with Sound Transit tax revenues and contributions from City of Tacoma. There is also a $75 million grant from the Federal Transit Administration plus $33 million in other federal and state grants.

Construction is expected to start in 2018.