A Locomotive is a machine used to haul a train. In the 19th century, locomotives were powered by steam. During the 20th century, there was a transition from steam to electric and diesel power.[1]
Major manufacturers of diesel locomotives in the United States include Electro-Motive Diesel and General Electric.
The Pennsylvania Railroad was a major user of electric locomotives until 1949 but then switched to diesels because they were more economical. In Europe, electric locomotives are still widely used.
In the 21st century, steam locomotives are rarely used in commercial service because of their high operating costs but preserved examples can still be seen on heritage railways.