<P> Diesel locomotives were first developed in Europe after World War I, and U.S. railroads began to use them widely in the 1930s and 1940s . Most U.S. roads discontinued use of steam locomotives by the 1950s . A diesel engine was expensive to build, but was less complex and easier to maintain than a steam locomotive, and required only one person to operate . This meant reduced costs and greater reliability for the railroads . Several companies developed fast streamliner trains, such as the Super Chief and the California Zephyr during the 1930s and 1940s . Their locomotives used either diesel or similar internal combustion engine designs . See Dieselisation in North America . </P> <P> Though electric railways expanded in Europe, they never reached the same popularity in North America . They were built primarily in the north - west and the north - east beginning in the late 19th century . While some railroads used electric locomotives for both freight and passenger trains, by the end of the 20th century most freight trains were pulled only by diesel locomotives . The Northeast Corridor, the most heavily travelled passenger line in the US, is one of few long lines currently operating with electrification . See Railroad electrification in the United States . </P> <P> Early forms of American railroad signaling and communication were virtually non-existent . Before telegraphs, the American railroads initially managed their train operations using timetables . However, there were no means of communication between drivers and dispatchers, and occasionally, two trains were sent on a collision course, or "cornfield meets ." With the advent of the telegraph in the 1840s, a more sophisticated system was developed that allowed the dissemination of alterations to the timetable, known as train orders . These orders overrode the timetable, allowing the cancellation, rescheduling and addition of trains . The earliest recorded use of train orders was by the Erie Railroad in 1851 . </P> <P> The development of the electrical track circuit in the 1870s led to the use of systems of block signals, which improved the railroads' speed, safety and efficiency . Mechanical interlockings, which prevent conflicting movements at rail junctions and crossings, were also introduced in the U.S. in the 1870s, after their initial development in Britain . </P>

How might the transcontinental railroad facilitate trade and communication