Life Cycle Ownership and Social Costs of Alternative Fuel Options for Transit Buses

Motivation. Transit buses provide short-distance public transportation service with multiple stops along fixed routes to serve citizens’ mobility needs. Transit agencies are more willing, compared to mainstream private... [ view full abstract ]

Motivation. Transit buses provide short-distance public transportation service with multiple stops along fixed routes to serve citizens’ mobility needs. Transit agencies are more willing, compared to mainstream private vehicle owners, to adopt alternative fuel vehicles because they are sensitive to fuel cost savings and have higher awareness and/or obligations to pursue sustainability. While a number of recent studies have analyzed alternative fuel options for transit buses, they did not take into account the externalities caused by by-products of bus operation, such as air emissions, to estimate full societal costs. In this paper, we estimate both life cycle ownership costs as well as life cycle social costs of greenhouse gases (GHGs) and criteria air pollutants (CAPs) for alternative fuel options for transit buses. In addition to a complete estimate of full societal costs using up-to-date emissions inventories and state-of-art marginal damage estimates, contributions of this paper also include a comparison between two types of BEBs (slow-charging and rapid-charging) and separate assessments for 40-foot buses and 60-foot buses.

Method. We consider the following fuel-vehicle options: a conventional bus powered by either diesel or a biodiesel blend (B20 or B100), a diesel hybrid-electric bus, a sparking-ignition bus powered by Compressed Natural Gas (CNG) or Liquefied Natural Gas (LNG), a BEB with slow charging in a garage, and a BEB with rapid charging along a bus route. We estimate life cycle ownership costs and social costs caused by greenhouse gases and criteria air pollutants emitted from the life cycle of bus operations. Life cycle ownership costs consist of four components: bus purchase costs, fuel costs, operation and maintenance costs (except fuels), and infrastructure costs. The metric used compare across options is annualized costs evaluated over a bus lifetime of 12 years. We choose the Port Authority of Allegheny County (PAAC) in Pennsylvania as a case study, but we also discuss how results change if assessment is done for a different region, and use sensitivity analysis to test the robustness of the findings.

Results. We find that only rapid-charging BEBs reduce ownership & social costs compared to diesel, while other options increase ownership & social costs. When external federal funding is available to pay for 80% of vehicle purchase expenditures, BEBs yield large reductions (39-45%) in ownership & social costs compared to diesel. Factors such as annual mileage, diesel price, discount rate, per-bus infrastructure cost, and electricity price determine BEBs’ cost reduction potential without external funding. But when external funding is available, BEBs’ advantages are robust. We find that BEBs are able to reduce CAP emissions significantly in Pittsburgh’s hotspot areas, where existing bus fleets contribute to 1% of particular matter emissions from mobile sources. We recognize that there are still practical barriers for BEBs, e.g. range limits, land to build the charging infrastructure, and coordination with utilities. However, favorable trends such as better battery performance and economics, cleaner electricity grids, and more experience likely favor use of BEBs where feasible.