1/16/2024 0 Comments Oakland 950 bus uniformThe following section describes the CA methods that are used to develop a model of the transit network to optimize. We hypothesize that user and agency costs are minimized in the design of a network, both costs and GHG emissions will be reduced. In this paper, we estimate the level of GHG emission reductions that can occur as a result of designing a transit network for optimal societal costs. This paper includes life-cycle GHG emissions that relate to infrastructure, maintenance, and vehicle manufacturing and operations, using emissions parameters estimated by Chester and Horvath (2009). Much of the literature related to transit emissions focuses on operating emissions and does not account for total life-cycle emissions ( Herndon et al., 2005 Puchalsky, 2005). Daganzo (2010) designed a transit system for Barcelona to be competitive with automobile in terms of travel time. Barcelona provides an excellent case study as a city for which a cost-optimal transit system has already been designed, requiring only the addition of emissions estimates. (2013), there is theoretically no cost associated with these reductions. Unlike the emissions reductions identified in Griswold et al. This paper addresses the unexplored question of how much GHG emissions can be reduced by moving an existing transit system to the cost-optimal point on the Pareto curve. A disadvantage of this approach is that any reductions in GHG emissions below the cost-optimal level come with a penalty in increased user travel time, which could send users to more polluting modes.Įxisting transit systems are not designed to optimize for costs, so it is likely that most systems are operating above the Pareto frontier, with both higher costs and emissions. They minimized costs subject to a GHG emissions constraint, and by varying the constraint, established the Pareto frontier of optimal system design, allowing them to examine the tradeoff between costs and emissions. (2013) took a different approach by incorporating emissions constraints into continuum approximation (CA) models that traditionally have only accounted for costs. Public transit systems that operate with low ridership have been shown to have higher per-passenger-kilometer emissions than the automobile ( Chester and Horvath, 2009). Technological approaches, retrofitting engines, or replacing vehicles, can be expensive, while increasing transit service to attract drivers to the system can backfire and cause a net increase in emissions ( Poudenx, 2008). Most efforts to mitigate GHG emissions from transit have focused on vehicle technology and mode shifts from private automobile ( Gallivan and Grant, 2010). Transportation contributes 28% of all greenhouse gas emissions in the United States and 23% worldwide ( Kahn Ribeiro et al., 2007 Environmental Protection Agency, 2014). With the increasing concern about global climate change, greenhouse gas (GHG) emission levels of the transportation sector have gained significant interest among researchers and policy makers. The analysis in this paper specifically focuses on the effects of bus technology with fixed ridership corresponding to the Barcelona case study, but the methods implemented could be easily applied to other transit modes in different cities. We, therefore, extrapolate and hypothesize that the optimization of transit networks in many cities would result in significant GHG emission reductions. Furthermore, the level of service to the user is not detrimentally affected and, in fact, it is slightly improved. In this case study, not only does the cost-optimal design lead to a 17% reduction in total costs, but even more notably, the optimal design leads to a 50% reduction in GHG emissions. The optimization of the system network design involves minimizing system costs and thereby determining optimal network layout and transit frequency. We demonstrate GHG emission comparisons between an optimized bus network design in Barcelona and the existing system. Utilizing continuum approximation methods and a case study in Barcelona, we show that efforts to decrease the costs of a transit system can lead to GHG emission reductions as well. In this paper, we examine how efficient bus transit networks can contribute to these reduction measures. The high contribution of greenhouse gas (GHG) emissions by the transportation sector calls for the development of emission reduction efforts. 4Department of Civil and Environmental Engineering, University of California Berkeley, Berkeley, CA, USA.3Division of Engineering, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates. 1Safe Transportation Research and Education Center, University of California Berkeley, Berkeley, CA, USA.
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