The multiple-unit traction control system was developed by Frank Sprague and first applied and tested on the South Side Elevated Railroad (now part of the Chicago 'L') in 1897. In 1895, derived from his company's invention and production of direct-current elevator control systems, Frank Sprague invented a multiple-unit controller for electric train operation. This accelerated the construction of electric-traction railways and trolley systems worldwide. Each car of the train has its own traction motors: by means of motor control relays in each car energized by train-line wires from the front car, all the traction motors in the train are controlled in unison.