Steam booster By Brian Schmidt | February 6, 2024 Email Newsletter Get the newest photos, videos, stories, and more from Trains.com brands. Sign-up for email today! Get Updates A Boston & Maine 2-10-2 steam locomotive is seen at Wooster, Mass., in an undated photo. The tender’s rear truck looks a little different from its front one because it’s a booster engine, an auxiliary locomotive designed to turn the main locomotive’s excess steam at slow speeds into extra traction to help get the train started. H.F. Harvey photo