This three-part report begins a series of studies mandated by Congress under various sections of the Railroad Revitalization and Regulatory Reform Act of 1976 to determine the best means for rehabilitating and revitalizing the nation's railroads. It is produced in accordance with Section 503(b) and is intended to provide a means of classifying the lines of the Class I railroads of the U.S. to serve a number of purposes under the Act. The prime purpose is to categorize the lines according to reasonable measures of priority so that investments in track can be directed where they will do the most good. Standards used by DOT for priority include traffic density, service to major markets, levels of capacity and national defense. Volume I established a preliminary set of categories and designation for public review, and contains three appendices. Volume II has individual line designations by state and a national map. Additions and corrections are in a separate pamphlet.