Mary Walton also invented a noise reduction system for elevated railroads in New York City. In the 1880s, many cities developed a mass transit system using noisy elevated trains. To reduce the noise, Mary Walton invented a sound-dampening system that cradled the track in a wooden box lined with cotton and then filled with sand.
She received U.S. patent #237,422 for the system on February 8, 1881, and later sold the rights to the Metropolitan Railroad of New York City.
