What are trains?

The railroad trains bring Ruth and Lucille's grandfather to Fingerbone and give him the job that allowed him to prosper and build a house there. The train also causes his death in the catastrophic derailment off the railroad bridge. Sylvie literally lives on the trains, jumping on boxcars and riding the rails as a transient. When the court threatens to take custody of Ruth, Sylvie escapes with her by crossing the railroad bridge, hopping a freight train, and bringing her into the transient lifestyle.