Performance of multiple alternatives to reduce carbon emissions for transit fleets: A real-world perspective

Transit agencies are always seeking opportunities to reduce fuel consumption, which typically provides simultaneous emissions reductions. However, the effectiveness and efficiency of fuel conservation and emission reduction alternatives differ as a function of local transit operating characteristics. The fact that emissions reductions from multiple alternatives are not necessarily additive further complicates these analyses. In selecting a set of alternatives, transit agencies need to evaluate multiple options simultaneously, and under agency-specific operating parameters. This paper presents the analysis of emissions reduction alternatives of eco-driving and purchasing new fleet with compressed natural gas, utilizing real-world operating data collected from the Metropolitan Atlanta Rapid Transit Authority (local transit) and the Georgia Regional Transportation Authority (express bus) fleets. Each individual emissions reduction alternative was first investigated for effectiveness individually and then in combination to assess cumulative impacts. The results show that the comparative performance of emissions reductions alternatives is highly dependent on vehicle operating characteristics, and thus the preferred alternatives, differ between different fleets. The analysis conducted for the Atlanta, Georgia region in the United States provides insight to how such modeling techniques can assist planning for future fleets given each agency's unique local conditions.