The first public proposal for such a line was made by the New York City merchant Asa Whitney in 1844. At that time the United States did not hold outright possession of land west of the Rockies, though it exercised joint occupation of the Oregon Country until 1846, when under a treaty with Britain it gained possession of the Pacific coast between the 42nd and 49th parallels. Whitney’s Railroad Convention proposed a line from the head of the Great Lakes at Duluth, Minnesota, to the Oregon Country. The Mexican War, by adding California, Arizona, and New Mexico to the American domain, complicated the matter greatly. North-South sectionalism intruded when it was appreciated that west of the Missouri any rail project would require a combination of federal and private efforts, the American practice. In the hope of resolving the regional conflict, the Corps of Topographic Engineers was authorized in 1854 to undertake the Pacific Railroad Survey, which studied almost all the potential rail routes in the West.

The survey on the 49th parallel was in the mid-1890s transformed into the Great Northern Railway. A near neighbour, the 47th parallel survey, had in the early 1880s been followed by the Northern Pacific Railway. The 41st parallel survey, only a partial investigation, sketched the alignment on which was to be built the first transcontinental railroad, the Union Pacific east of Great Salt Lake and the Central Pacific west thereof. The 35th parallel route became the Rock Island line from Memphis to Tucumcari, New Mexico, and westward from there the Atchison, Topeka, and Santa Fe Railway to Los Angeles. The southernmost route, the 32nd parallel, was to run from Shreveport, Louisiana, across Texas and then, through the Gadsden Purchase of 1853, to San Diego; this route became the Southern Pacific line from Los Angeles to El Paso.

Construction began in 1862 of the 41st parallel route, which had been selected to receive federal grants, but because of the outbreak of the Civil War relatively little was accomplished on the Union Pacific Railroad before the end of fighting in 1865. In California, little affected by the war, construction was more rapidly advanced. By 1865 the original juncture of the Central Pacific and Union Pacific was moved eastward; the meeting took place on May 10, 1869, at Promontory, Utah.

The opening of the Pacific railroad in 1869 demonstrated that the market for the profitable operation of such a line still lay somewhat in the future: one eastbound and one westbound train a week were adequate to meet the demands of traffic. It took almost a generation before additional rail lines to the west coast seemed justified. In 1885 the Santa Fe reached the Los Angeles basin and the Northern Pacific Railway reached Puget Sound. Each western railroad now had to shape a new economic and geographic strategy. In place of the natural territory gained through monopoly the western lines tried to accomplish regional ubiquity, under which the Southern Pacific (originally the Central Pacific), the Union Pacific, or the Santa Fe attempted to have a network of rail lines that reached to the Pacific Southwest, the Pacific Northwest, and northern California; only the Union Pacific succeeded. The American rail network was essentially complete by 1910 when the last transcontinental line, the Western Pacific Railroad to Oakland, California, was opened.

Advances in traction systems

Diesel-electric locomotives appeared in the 1920s. Individual locomotive units provided up to 5,000 horsepower, a figure equal to all the steam-engine power in the United States in 1800. Locomotive units could be multicoupled and operated by a single engineer. It became routine to run “unit trains” containing 100 to 150 freight cars, semipermanently coupled together and operating over a single long run carrying a single commodity, most commonly coal but also other minerals or grains. Not only did diesel-electric locomotives make such routinization of freight operation possible but they also reduced labour demands greatly. Refueling engines required only pumping heavy fuel oil at infrequent intervals; locomotives frequently ran coast-to-coast with only changes of crew and refueling.

In the first third of the 20th century electrification of standard railroads (which came first on the B&O in 1895) proceeded. Never as widespread as in Europe, electrification today is particularly associated with the northeastern United States. This regional concentration of electrification has meant that only between Boston and Washington, D.C., where the federally assembled Amtrak system owns the infrastructure, is there potential to seek easy high-speed rail development. Experimental high-speed projects began in this northeast corridor in the 1960s when both the Pennsylvania Railroad with its electrically operated Metroliners and the New Haven Railroad diesel-electric Turbotrains began running, and since 2000 Amtrak has run its electric Acela Express trains between Boston and Washington. The Metroliners (phased out in 2006) attained speeds of 200 km (125 miles) per hour in the best sections, while the Acela Express trains are capable of reaching speeds in excess of 240 km (150 miles) per hour—though average operating speeds over the entire route are far lower, generally about 120 km (75 miles) per hour.

Railway company mergers

Throughout the 20th century the ownership and organization of U.S. railroads changed. Mergers were common, and the bankruptcy of Penn Central Railroad in 1970 became the nucleus around which a number of northeastern railroads were joined into a nationally owned Consolidated Rail Corporation (Conrail), established by the federal government under the Regional Rail Reorganization Act of 1973. The new company’s tracks extended from the Atlantic Ocean to St. Louis and from the Ohio River north to Canada. Although it was set up to be an independent profit-making corporation, in its early years, even with the aid of federal loans, it lost more than the bankrupt lines had lost before consolidation. In 1981 Conrail turned a profit for the first time, and in 1987 the government put its stock up for sale to the public. After several years of profitable operation, the assets of the company were purchased in the late 1990s by two other rail companies, CSX Corporation and Norfolk Southern Corporation.

Within months after the Penn Central bankruptcy, a number of railroads applied for Interstate Commerce Commission permission to abandon intercity passenger service. From about the early 1960s, the railroads had lost millions of dollars annually on their passenger lines as a result of a steady decline in their ridership and increases in their operating costs. In 1950, for example, there were approximately 9,000 passenger trains in service, and these lines carried just under 50 percent of all intercity traffic. By 1970, however, there were only about 450 trains still in operation, with a total share of the passenger traffic amounting to a mere 7 percent. Freight service was still modestly profitable, but passenger service was, as virtually everywhere else in the world, possible only with substantial government subsidies. At this point Congress founded the National Railroad Passenger Corporation, or Amtrak, which in 1971 assumed control of passenger service from the nation’s private rail companies. More than a century earlier, land grants had been given to railroads to spur completion of the transcontinental line, but the creation of Amtrak marked the first time that rail passenger service had received any form of direct financial assistance from the U.S. government. The new corporation was set up to pay the railroads to run their passenger trains and also compensate them for the use of certain facilities, including tracks and terminals. It bore all administrative costs, such as those incurred for the purchase of new equipment, and managed scheduling, route planning, and the sale of tickets. Income from passenger fares has never been sufficient to pay for operating and capital-improvement costs, and, as a result, Amtrak has regularly received subsidies from the federal government—in addition to constant scrutiny of its operating and budgetary practices and periodic threats from Congress to reduce or even eliminate funding.

By the turn of the 21st century, rail was estimated to account for only about 1 percent of intercity traffic in the United States. Amtrak was responsible for some 33,800 km (21,000 miles) of track around the country, though by far most of its ridership was found in so-called urban corridors, short- or medium-distance routes that linked centres of high population. The Northeast Corridor in particular became Amtrak’s most important service area. In this megalopolis, extending roughly from Boston through New York City to Washington, D.C., the dense population presented a market that could be exploited by a fast modern rail passenger service. In 1976 Amtrak took over the route, assuming direct ownership of the tracks and facilities. At the same time, a federally funded Northeast Corridor Improvement Project was begun to upgrade the route for high speed and extend electrification over the entire route. By 1991 the route between New York and Washington could be run at high speed by Metroliner, which were hauled by lightweight 7,000-horsepower electric locomotives of Swedish design. The Metroliner was replaced between 2000 and 2006 by the Acela Express, whose passenger cars and electric power cars were built by Bombardier Inc., a Montreal-based builder of aircraft and transportation equipment, in partnership with the French company Alstom, a manufacturer of electric motors and other power equipment. In the face of severe airline shuttle competition, Amtrak’s frequent train service has become the dominant public passenger carrier in the New York–Washington corridor. In 2010 Amtrak claimed more than one-half of the combined rail and air passenger market between the two cities and also between New York and Boston.