Railroads or railways are a means of transporting freight (goods) and passengers (persons) on vehicles guided by tracks that constrain movement and eliminate steering common to all means of road transport. Railroad transport imparts lower frictional resistance to a wheeled vehicle than a road, increasing the efficiency of transport and reducing energy consumption. Modern railroads are long stretches of metal rails with traffic management systems for rail vehicles that include locomotives, train cars (including self-propelled units known commonly as electric multiple units [EMU]) that constitute freight trains and passenger trains, and other vehicles responsible for the maintenance and service of railways they transverse.
Railroad infrastructure include the railroad tracks (metal, usually steel rails and timber or concrete ties), electrification systems, signaling systems, train and railroad inspection systems, train stations, and other operational support facilities. Intelligent transportation systems (ITS) represent IT systems running parallel to railroads and leveraging existing electrification and signaling systems.
Railroads have expanded in application from short-distance industrial conduits, to long-distance freight and passenger transport through steam power, to networks of urban, regional and continental railroads responsible for transporting commuters, passengers, livestock, freight and other goods. Through electrified subway and metropolitan raised rail trains, railroads are now responsible for mass transit. Railroads have trailed public highways and streets in investment in the United States for decades, although rising interest in reducing transportation fuel consumption and relieving traffic congestion has led the United States and other countries to consider high speed rail (HSR) and other rail modernization projects.