The Role of Public Transit Service as a Greenhouse Gas Emissions Reduction Strategy

Focus Area

Climate Change


Air Quality, Environmental Process







Research Idea Scope

Early federal transit-related greenhouse gas (GHG) efforts such as the American Recovery and Reinvestment Act’s (ARRA) Transit Investments for Greenhouse Gas and Energy Reduction (TIGGER) grants enable transit agencies to reduce GHG emissions through the purchase of more fuel-efficient vehicles among other capital investment strategies. However, these strategies do not address the more critical fact that even a fuel-inefficient diesel bus produces dramatic GHG savings over the same number of passengers in private automobiles (assuming reasonable levels of ridership).
·      While the notion of public transit as a “green” or more environmentally friendly mode of transportation is established in the popular consciousness, this idea tends to be most directly associated with rail service, and particularly with extremely capital-intensive new rail investments.
·      Although there is an important role for rail investments, less capital-intensive solutions, such as providing higher levels of service on existing bus routes along with ancillary enhancements to the transit experience, may offer opportunities for even more significant environmental benefits. For example, service with 20-minute headways will be much more attractive to discretionary riders than service with hourly headways. However, it will also be more costly in the short run (in terms of operating costs) while ridership develops. If short-term operating costs can be overcome, a dense network of high-quality, frequent bus routes can have significant impacts in terms of changing trip patterns, reducing local vehicle miles traveled, and supporting transit-friendly development.
·      Research may find that expanding fleets and enabling higher levels of service (while absorbing short-term operating deficits) may be more cost-effective in reducing GHG emissions from the transportation sector than greening transit vehicles. In this case, it would be more effective for federal transportation dollars seeking GHG benefits to be spent in this way. Such an investment program may form an important element of broader federal climate change policies and investments.
This project would explore the nexus between transit service and regional greenhouse gas emissions, with the aim of establishing a simple yet rational method for estimating and comparing the GHG impacts of various operations investments. As envisioned, this project would have two main components: first, development of a method to explore the efficacy of the proposed concept (i.e., is it more climate-friendly to expand fleets with additional standard buses, or to replace existing fleets with highly fuel-efficient buses?). The second component would be an exploration of the data needs and method for this tradeoff to be calculated at the local or regional scales, in conjunction with the establishment of proposed funding formulas and performance measures. To be viable, the proposed funding framework should balance robustness with simplicity in order to be manageable by transit agencies, state DOTs, and/or MPOs of all scales.
Related Work
Todd Davis and Monica Hale (2007), Public Transportation’s Contribution to Greenhouse Gas Reduction, American Public Transportation Association. This study was conducted for the American Public Transportation Association (APTA) with funding provided through TCRP Project J-11/Task 2.
The proposed research is timely in order to contribute to the ongoing congressional and federal dialogue on new climate change strategies, policies, and investments.

Urgency and Payoff

The desired project outcome would:
·      Refine an understanding of the linkage between public transit and greenhouse gas emissions for policymakers and members of the public;
·      Define ways to estimate a GHG value for pounds of CO2 per passenger mile traveled, considering local factors. This would contribute to the definition of performance measures and help to rationalize operational investments within the broader context of climate change policy (such as “cap and trade” markets);
·      Review the existing literature on Life Cycle Analysis (LCA) protocol to assess its viability in the modeling process for transit GHG impact documentation;
·      Establish a framework for making ‘GHG-smart’ service investments (i.e., routes where buses are full and there is demonstrable additional demand? Provide Bus Rapid Transit (BRT)-like route enhancements to attract discretionary riders and maximize mode shift?);
·      Detail alternatives for how GHG-related operating assistance could most effectively be provided at the state, metropolitan, or transit agency levels, and establish suggested alternatives for funding sources (and linkages with other climate change programs) as well as performance measures for funding received;
·      Result in an outline for the establishment of new federal formula-based operating assistance in the context of broader federal climate change policies.
This research will refine an understanding of the relative GHG benefits of “greening” transit fleets versus modernizing, optimizing, and selectively expanding operations. The resulting project report will blueprint how, through optimizing existing resources, route planning, improved client services, and investments in operations and maintenance, a transit agency can establish an operational baseline that will result in lower GHG generation per passenger mile traveled (PMT).
 Drawing on that baseline, the report will suggest best practices for “green” system investments that will help federal agencies to make GHG-related transit investments in a more cost-effective way.

Suggested By

RNS. Sponsoring Committee: A0020T, Special Task Force on Climate Change and Energy Source Info: Special Task Force on Climate Change and Energy January 2010 Workshop