Ever since her days with folk revivalists Carolina Chocolate Drops, Rhiannon Giddens has championed the marginalised or suppressed elements of American musical tradition. Now artistic director of the Silkroad Ensemble, a multi-ethnic, 13-strong troupe founded in 2000, Giddens has overseen a history of America’s coast-to-coast railroad, or more particularly the army of workers who built it. Most were Irish, African American, Chinese and Japanese, while Native Americans found their lands snatched away. It’s a substantial project, including a podcast and museum expos alongside this album – recorded live – inspired by or drawn from the times. Giddens, with her opera-trained voice, grabs the glory with renditions of Swannanoa Tunnel, an Appalachian ballad about a route that cost an estimated 300 lives, and Steel-Driving Man, about the fabled John Henry. The record is, however, mostly instrumental, drawing on a well-manicured mix of cellos, banjos and ethnic instruments. It’s all impeccably played, even if the link to railroads and navigation is sometimes unclear; a tabla solo does not evoke a prairie, though Congolese guitarist Niwel Tsumbu does so on Milimo. There is sorrow from Native American activist Pura Fé, who also voices a moving blues, Have You Seen My Man?, before the set climaxes in a collective gospel blaze. Classy, but only intermittently evoking bygone times.