Rail transportation has been around since the early nineteenth century. It replaced America's network of canals, inland water steam navigation and other early forms of transportation. However, it has yet to be replaced as a key facet in America's transportation portfolio. Given rail transport's tremendous efficiency and cost effectiveness, there are many different forms of rail in use today. Ranging from small to large, they all serve a basic purpose: to move people and freight. Here is a basic overview of the railroad industry's main components.

Class I Freight Carrier: Generally focused on moving freight, a Class I railroad is defined by the Surface Transportation board as having in excess of $250 million dollars in annual revenue. Class I railroad companies own and maintain a huge network of routes connecting different locations and mainline tracks spanning several states. They possess a large fleet of locomotives and railcars suited to shipping many different kinds of materials. The Class I carriers are Canadian Pacific Railway, Norfolk Southern Railway and CSX, Union Pacific, BNSF, Canadian National and Kansas City Southern. Collectively, these companies make up a large majority ownership of all operable tracks in the United States.

Class II or “Regional” Freight Carriers: These railroads are smaller than their Class I brethren in both track-miles and revenue. A regional railroad is classified as earning less than $250 million but more than $20.5 million in annual revenue. Regional railroads often own mainline track routes to move goods long distances but often have a network of slower speed secondary tracks that branch out and connect with factories and mills that may not generate or receive as many shipments as industries on a Class I system might. Regional railroads play an important role by providing small companies with access to the major rail infrastructures across America and generating traffic for Class I railroads. Some examples of Regional carriers in America are the Reading & Northern Railroad, Wheeling & Lake Erie and the Maine, Montreal & Atlantic System.

Class III or “Shortline” Freight Carriers: Short-line railroads are often the smallest of the point-to-point rail systems in America. Their trackage territory can range from only a few miles and upward. Their official classification is contingent upon annual revenues being less than $20 million dollars annually. A large percentage of American short-line railroads are slower speed “branch line” tracks that were sold off by larger railroads. Short-lines often only have a few locomotives but can provide greater levels of attention to customers on its lines than a larger railroad carrier with many customers and lines. Some examples of short-line railroads in America are Lehigh Railway (56 track miles), Towanda Monroeton Shippers Lifeline (6 track miles), and Delaware-Lackawanna (85 track miles).

Class I National Passenger Carrier: After most railroads were permitted to abandon passenger service in the mid twentieth century, Amtrak was formed by the US Government to preserve passenger service with federal funding given its unprofitable nature. Today, Amtrak officially qualifies as a Class I carrier due to the level of revenue it receives. It utilizes a network of its own tracks and over track usage rights on other railroads to provide service in most regions across the country.

Regional Commuter Carrier: Also known as Commuter Rail, Virginia Railway Express finds itself in this category. These carriers can either operate on a network of privately held right-of-way or can operate over host railroad territory. Regional Commuter carriers are generally found around dense urban areas. Regional carriers generally own or lease their own fleet of specially built passenger equipment capable of speeds of up to 79 mph and most often operate under partnerships with a transportation authority or government agency. Some other examples of Regional Commuter carriers would be the Trinity Railway Express, based in Texas, SEPTA Regional Rail Division, based outside of Philadelphia, and New Jersey Transit Regional Rail, based in Northern New Jersey.

Closed System Rapid Transit: This system will most often operate on its own network of trackage within a city or connecting two major population centers. The defining difference between this system and other previously listed systems is train frequency. Within a rapid transit network, there are generally a large amount of connection options and routine train arrivals and departures without interference from other types of trains (closed system). The equipment is generally electrically propelled, versus conventional diesel-electric locomotive use. An example of this type of system, locally, is Metro. Nationally, another example is New York's MTA.