Diesel Multiple Units in 21st Century North America: Comparative Survey and Evaluation of Services, Demand, and Cost

U.S. officials working with finite resources to build and operate new fixed-guideway transit services grow more creative every year, finding ways to offer new and expanded services with fixed or declining resources. One creative approach to the development of new urban passenger rail services has been to operate on tracks shared with light-density freight services. Most services have used conventional commuter rail passenger rolling stock for these services, but, in some circumstances, this relatively heavy equipment has been inappropriate, and officials have been forced to consider sharing freight tracks with lighter, shorter trains. Some of these trains have been conventional electric light rail cars, but since the turn of the 21st century, five new U.S. services using self-powered diesel rail cars (historically called diesel multiple units, or DMUs) have opened to offer new travel options in Texas, California, New Jersey, and Oregon. FTA has termed these new shared-track DMU services “hybrid rail.” This paper reviews the circumstances and conditions that gave rise to the development of these hybrid DMU systems. The paper then reports the results of a study that used federally reported data to conduct a survey and evaluation of these services as compared with electric light rail and conventional commuter rail services. The analysis found that the new DMU systems tended to function in a new service stratum between commuter and light rail that served the needs of markets that neither of those traditional modes was well suited to address.