with California on the Pacific coast. Finished on May 10, 1869, at the Golden spike event at Promontory Summit, Utah, it created a nationwide mechanized transportation network that revolutionized the population and economy of the American West, catalyzing the transition from the wagon trains of previous decades to a modern transportation system. It achieved the status of first transcontinental railroad by connecting myriad eastern U.S. railroads to the Pacific Ocean. However it was not the world's longest railroad, as Canada's Grand Trunk Railway (GTR) had, by 1867, already accumulated more than of track by connecting Portland, Maine, and the three northern New England states with the Canadian Atlantic provinces, and west as far as Port Huron, Michigan, through Sarnia, Ontario. Authorized by the Pacific Railway Act of 1862 and heavily backed by the federal government, the first transcontinental railroad was the culmination of a decades-long movement to build such a line and was one of the crowning achievements of the presidency of Abraham Lincoln, completed four years after his death. The building of the railroad required enormous feats of engineering and labor in the crossing of the Great Plains and the Rocky Mountains by the Union Pacific Railroad (UP) and Central Pacific Railroad, the two federally chartered enterprises that built the line westward and eastward respectively. The building of the railroad was motivated in part to bind the Union together during the strife of the American Civil War. It substantially accelerated the populating of the West by homesteaders, leading to rapid cultivation of new farm lands. The Central Pacific and the Southern Pacific Railroad combined operations in 1870 and formally merged in 1885; the Union Pacific originally bought the Southern Pacific in 1901 and was forced to divest it in 1913, but took it over again in 1996. Much of the original roadbed is still in use today and owned by UP, which is descended from both of the original railroads. Rail gauge selection Many Canadian and U.S. railroads originally used various broad gauges, but most were converted to by 1886, when the conversion of much of the southern rail network from gauge took place. This and the standardization of couplings and air brakes enabled the pooling and interchange of locomotives and rolling stock. Impact of railroads on the economy The railroad had its largest impact on the American transportation system during the second half of the 19th century. The