Light Rail/Rapid Transit: New Approaches for the Evaluation of Energy Savings, Part I - Life-Cycle Cost from Synthetic Routes/Operational Models

The energy-saving benefits of new traction technologies for light rail/rapid transit systems must be evaluated on the basis of life-cycle cost, which includes both purchase cost and energy consumption. Rigorous energy consumption evaluations previously have not been possible because of the lack of 1) a practical basis for comparing the energy consumption of different transit car/traction systems and 2) information concerning the receptivity of transit systems to available regenerative braking energy. New approaches are described that will provide a practical basis for energy consumption comparisons. Techniques for solving the complex computational problems of the receptivity of large systems are described in a companion paper [16]. Overall, a systematic approach for comparing the energy consumption of different traction systems on the basis of equal work performed (operational model) is presented. The techniques described will allow a total cost figure based on purchase price plus energy consumption to be calculated for each type of transit car on a given property basis. The concept of a synthetic route, the energy equivalent of specific transit routes under study, is introduced for comparing energy consumption values during the bidding stage, prior to system selection. This concept, which significantly simplifies the computation task, was used in predicting the annual traction energy consumption of the Toronto Transit Commission's (TTC) Presidents' Conference Committee (PCC) streetcar fleet. The computations indicated that retrofitting the fleet with fully regenerative chopper systems would reduce energy consumption by more than 50 percent. A more generalized approach, utilizing an operational model, offers additional advantages in power flow studies of transit systems to optimize substation design, feeder requirements, and fleet traction system mixtures. An evaluation using this approach predicted that the peak rush-hour power demand for the TTC fleet would be reduced by 48 percent if the streetcars were converted to regenerative chopper systems, or by a larger amount if the conversion was to idealized flywheel traction systems. Power distribution loss data also were derived for the traction systems studied.