Tradeoffs between costs and greenhouse gas emissions in the design of urban transit systems

Abstract

Recent investments in the transit sector to address greenhouse gas emissions have concentrated on purchasing efficient replacement vehicles and inducing mode shift from the private automobile. There has been little focus on the potential of network and operational improvements, such as changes in headways, route spacing, and stop spacing, to reduce transit emissions. Most models of transit system design consider user and agency cost while ignoring emissions and the potential environmental benefit of operational improvements. We use a model to evaluate the user and agency costs as well as greenhouse gas benefit of design and operational improvements to transit systems. We examine how the operational characteristics of urban transit systems affect both costs and greenhouse gas emissions. The research identifies the Pareto frontier for designing an idealized transit network. Modes considered include bus, bus rapid transit (BRT), light rail transit (LRT), and metro (heavy) rail, with cost and emissions parameters appropriate for the United States. Passenger demand follows a many-to-many travel pattern with uniformly distributed origins and destinations. The approaches described could be used to optimize the network design of existing bus service or help to select a mode and design attributes for a new transit system. The results show that BRT provides the lowest cost but not the lowest emissions for our large city scenarios. Bus and LRT systems have low costs and the lowest emissions for our small city scenarios. Relatively large reductions in emissions from the cost-optimal system can be achieved with only minor increases in user travel time.

Planning hierarchical urban transit systems for reductions in greenhouse gas emissions

“…On the other hand, transit agencies of large cities are more likely to deploy hierarchical transit systems and with mass transit modes such as metro as the trunk technology. Our results are different from the findings in Griswold et al (2013) where metro was suboptimal in all the city scenarios, which was a limitation of the trunk-only transit model. Incorporating a feeder system increases the relative competitiveness of mass-and capital-intensive transit technology with respect to both cost minimization and emissions savings.…”

“…The formulation of the problem builds on the work of Sivakumaran et al (2014), Griswold et al (2013) and Griswold et al (2014). The mathematical formulation consists of optimizing the transit system design to achieve the lowest total costs and transit emissions possible.…”

Assessment of alternative fuel and powertrain transit bus options using real-world operations data: Life-cycle fuel and emissions modeling

“…This application is particularly useful for agencies that own a limited number of alternative fuel/powertrain vehicles and desire to use them efficiently. Using the FEC can help agencies maximize fuel savings by assigning alternative fuel vehicles to the routes where the vehicle type is the most advantageous, capturing environmental and cost benefits from design and operational improvements in combination with vehicle technologies [52]. Finally, the FEC allows agencies to evaluate fuel and emissions savings based on an entire day or week's operations.…”

A Transit Technology Selection Model

“…These two recent studies demonstrate the importance of including emissions data in the decision-making tools for LRT and BRT projects. While there has been effort by researchers to quantify and compare the indirect costs of transit emissions in cost models (Keeler and Small 1975;Parajuli and Wirasinghe 2001;Wang 2011;Griswold et al 2013), our model is distinct in that does not attempt to convert the emissions into an annual cost, as this quantification includes additional assumptions for parameters. Rather, we present the annual emissions and allow the decision-maker to determine how influential environmental impact is on the overall transit technology selection.…”