A cargo train containing multiple cars used for carrying hydrochloric acid (red and white painted tank cars in this image) is moved between rail yards near Chicago's Chinatown neighborhood in fall 2021. 2.21 million carloads of chemicals-- including hazardous materials such as chlorine gas, strong acids, and ammonia, as well as non-hazardous substances such as potassium chloride-- were hauled by U.S. freight railroads in 2021 according to the Association of American Railroads.