Amtrak is no longer required by law, but is encouraged, to operate a national route system.[57] Amtrak has some presence in all of the 48 contiguous states except Wyoming and South Dakota.[58] Service on the Northeast Corridor, between Boston, Massachusetts, and Washington, D.C., as well as between Philadelphia and Harrisburg, Pennsylvania, is powered by overhead wires; for the rest of the system, diesel locomotives are used. Routes vary widely in frequency of service, from three trips weekly on the Sunset Limited, from Los Angeles, California, to New Orleans, Louisiana, to weekday service several times per hour on the Northeast Corridor, from New York City to Washington, D.C.[59] Amtrak also operates a captive bus service, Thruway Motorcoach, which provides connections to train routes.
The most-popular and heavily used services are those running on the Northeast Corridor (NEC), which include the Acela Express, and Regional. The NEC serves Boston, Massachusetts; New York City; Philadelphia, Pennsylvania; Washington, D.C.; and many communities between. The NEC services accounted for 10.0 million of Amtrak's 25.7 million passengers in fiscal year 2007.[60] Regional services in California, subsidized by the California Department of Transportation are the most popular services outside of the NEC and the only other services boasting over one million passengers per annum. The Pacific Surfliner, Capitol Corridor and San Joaquins services accounted for a combined 5.0 million passengers in fiscal year 2007.[61]
Four of the six stations busiest by boardings are on Amtrak's NEC: New York (Penn Station) (first), Washington (Union Station) (second), Philadelphia (30th Street Station) (third), and Boston (South Station) (sixth). The other two of the top six are Chicago (Union Station) (fourth) and Los Angeles (Union Station) (fifth).[62]
Amtrak trains have both names and numbers. Train routes are named to reflect the rich and complex history of the routes and the areas traversed by them. Each scheduled run of the route is assigned a number. Generally, even-numbered routes run northward and eastward, while odd-numbered routes run southward and westward. Some routes, such as the Pacific Surfliners, use the opposite numbering system, inherited from the previous operators of similar routes, such as the Santa Fe Railroad.
