 Many of them continue to have an important role in freight transportation and some like the Transsiberian Railroad even have passenger trains going from one end to the other.A transcontinental railroad in the United States is any continuous rail line connecting a location on the U.S. Pacific coast with one or more of the railroads of the nation's eastern trunk line rail systems operating between the Missouri or Mississippi Rivers and the U.S. Atlantic coast.The first concrete plan for a transcontinental railroad in the United States was presented to Congress by Asa Whitney in 1845.