Amtrak

Amtrak, or more precisely The Natioanl Railroad Passenger Company, is the quasi public company which operates passenger trains in the United States. It operates in every U.S. state except Alaska, Hawaii, and Wyoming.

Background and history
Prior to 1971, passenger trains were operated by what we refer to as freight railroads. However, due to the mounting profit loss to the private railroad companies, there was an attempt to get out of the passenger business. On October 30, 1970 legislation  was passed by the 91st congress authorizing Amtrak. On May 1st, 1971, Amtrak begin hauling it's first passenger trains.

Current Status
Amtrak is the only intercity passenger train corporation in the United States. It, also, operates a number of commuter trains, particularly in The Northeast Corridor.