Assessment of Sustainability of Locomotive Propulsion Technologies

Abstract: United States has the largest railroad network in the world with a total mileage of over 160,000 by the year of 2023. This system has been considered one of the safest and most cost-efficient transportation infrastructures in the world. As of today, the growing threat of global warming has created an urgent need to reduce the carbon footprint of transportation infrastructure. For the railroad industry, approximately 99% of the locomotives are operating on diesel, which is a nonrenewable fossil fuel and can contribute considerable greenhouse gas emission to the planet. The efforts to achieve sustainability are primarily focused on two approaches. One is to adopt alternative fuels, such as natural gas, biofuels, or hydrogen. The other option is to electrify existing railroads. This paper provides a comprehensive life cycle assessment (LCA) regarding these potential options encompassing the economic, environmental, and social impacts. A functional unit is defined as the energy demand for a 500-mile railroad with a design horizon of 20 years . The amount of fuel or electricity consumption can thus be estimated based on energy efficiency. For environmental impacts, the metrics include global warming potential (GWP) and cumulative energy consumption (CED). For economic considerations, life cycle costs (LCC) are used to quantify the impacts. For social impacts, the stakeholder acceptance and safety concerns are discussed in a qualitative manner. It was found that the GWP, CED, and LCC are largely concentrated in the use phase rather than in the manufacturing of the infrastructure or end of life stage. For alternative fuels to diesel, natural gas has the lowest life cycle cost, which is possibly a consequence of the shale revolution in the 2000s. Hydrogen can greatly lower overall energy consumption, while biofuel is the most advantageous in reducing carbon footprint . For electrified railroads, the performance will largely depend on the type of power plants providing electricity, which in this study was hard coal, natural gas, nuclear, or hydropower. It was found that if the electricity of railroads is provided by a hydropower plant, the environmental impact will be reduced to the minimum. However, if the electricity is derived from hard coal, the carbon footprint will be even greater than conventional diesel locomotives. For social considerations, it is foreseen that the safety concern of natural gas and hydrogen can be a great challenge for its adoption by the U.S. railroad industry. The potential attitude and preferences of railroad companies, labor unions, government, academics, and the public are also discussed in detail. The sustainability assessments of this paper are based on data from academic publications, conference proceedings, and governmental resources such as U.S. Energy Information Administration (EIA), Environmental Protection Agency (EPA), and Federal Railroad Administration (FRA).