There are two main types of railroads: major railroads and short lines. With the consolidation in the early part of the 20th century of many smaller lines into larger, more extensive systems, there evolved a limited number of major railroads that operate trains over long distances. Both major and short lines operate freight lines and passenger lines. Railroads are also separated by passenger and freight lines, with freight lines further divided into three classes.

Passenger lines include commuter railroads, which generally connect cities to the surrounding suburbs, and Amtrak, which travels between cities. Many large urban areas also rely on rail transport, such as subways, for intercity transportation. Class I freight lines, of which seven operate in the U.S., have at least $490 million in annual operating revenue. Class II are those freight lines with operating revenue between $36.6 and $457.9 million; there are 21 in the U.S. There are about 550 Class III rail lines—those with revenue below $36.6 million—in the U.S., which includes short line railroads, local rail systems that connect to the main railroads.

The major railroad systems in the United States are organized much like any other business, with stockholders, a board of directors, and a chief executive officer (CEO). Like most other large corporations, the typical large railroad is divided into various segments, or divisions, that perform tasks related to certain aspects of the business. Individual railroads may assign different names to divisions, but the four basic career areas in the railroad industry are transportation, communications, administration, and maintenance.

The majority of railroad employees work in the transportation department. Workers in the transportation department are responsible for the actual operation of the locomotives and the trains. Conductors and engineers, who work on the train while it is en route, are the most common employees in this category. Other employees, called switchyard employees, work in rail yards along the train route to form trains by coupling and uncoupling cars and directing them along the right tracks. Transportation employees who work in switchyards spend most of their time in one place, while those who work on trains while they are en route spend much of their working time traveling. Many railroads, such as the Norfolk Southern, further classify transportation department employees as agreement or labor employees because most are represented by a union and their benefits and compensation are negotiated.

Every major railroad has an extensive communication network, with dispatchers working in central locations to monitor the progress of each train. These communications workers receive and pass on information to the crews of trains that are en route. For example, a communications worker might notify a train crew about the location of other trains or the condition of the upcoming tracks. Since the 1980s, computers have handled most of the routine dispatching functions, allowing a single dispatcher or operator to oversee and direct large segments of a railroad. Some railroads use a system of transponders in the track, which transmit train location and speed directly to computers in the dispatch office. Other railroad dispatchers receive the same information via radio signals from satellites. In either case, dispatchers are able to easily follow the progress of various trains and are able to arrange and issue orders for train movement from thousands of miles away.

The administrative department within a railroad is very similar to administrative departments in other large industries. Railroads have a variety of clerical and office personnel, with secretaries and clerks performing a range of tasks. Also found within the administrative segment of the industry are more specialized departments performing individual functions.

Most large railroads, for example, have a sales and marketing department, which works with present and potential customers to sell rail services. Since most rail business is in freight, employees in sales and marketing departments work primarily with companies that need to ship their product to distant places. Workers in this department might develop marketing brochures and campaigns, meet regularly with existing clients to maintain good relations, or write proposals and make presentations to potential clients. For railroads that have passenger service, sales and marketing workers might attend trade shows and communicate with travel agents or tour packagers to promote their rail service. Workers in sales and marketing typically work out of a railroad's headquarters.

Another subdivision of the administrative category is shipping and receiving. Workers in shipping and receiving are responsible for recording information about cargo that is being sent, making sure that it is placed in the appropriate car, tracking its progress, and making sure that it is received, undamaged, at the correct destination. In passenger service, instead of performing shipping and receiving tasks, workers take reservations, answer passenger questions, and sell tickets.

There are many other types of administrative services that are also necessary to the running of a railroad. Large railroad systems have their own attorneys and their own accountants. Computer programmers and analysts maintain the railroads' sophisticated management information systems. Workers in the personnel department are responsible for hiring, training, evaluating, and maintaining paperwork on all the railroad's employees. Finally, a supervisory staff consisting of several levels of managerial employees tends to the financial and policy decision-making and the employee supervision for the entire operation.

Making certain that engines, freight and passenger cars, tracks, signals, and communications equipment are in perfect working order is the responsibility of the maintenance department. Maintenance workers install and maintain signal equipment, repair locomotives and train cars, and monitor miles and miles of track to ensure they are safe for travel. In trains with passenger service, additional workers are needed to clean the cars, restrooms, kitchens, and dining areas. Workers in the maintenance side of the business work in almost every state, both in small towns or large cities. If they are responsible for maintaining many miles of track, they may spend part of their time away from home.

In addition to the major railroads, short-line (or feeder) railroads still exist as well. There are about 603 of these smaller railroads, found in 49 states. Short-line railroads employ 17,800 people, serve 10,000 customers, and haul 29 percent of freight rail in the U.S., according to the American Short Line and Regional Railroad Association. In addition, short lines have grown from 8,000 miles of track in 1980 to more than 47,500 miles of track today.

Short-line railroads do not have the number or variety of jobs that the large systems do, however. While someone must perform the duties of engineer, conductor, signal worker, dispatcher, and shipping and receiving clerk, in smaller systems several of these duties may be performed by the same person. Also, most short-line railroads do not have the need for a full-time attorney, accountant, or computer specialist. While some short lines may have employees who perform sales and marketing functions, they typically do not have entire departments devoted to those tasks.

An additional category of railroad employment includes government employment, which can range from the subway and streetcar operators who work for municipally operated lines to inspectors for the Federal Railroad Administration. Federal railroad inspectors inspect rail lines for compliance with federal regulations and conduct accident investigations.