Abstract
The high contribution of greenhouse gas (GHG) emissions by the transportation sector calls for the development of emission reduction efforts. In this paper, we examine how efficient bus transit networks can contribute to these reduction measures. 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. We demonstrate GHG emission comparisons between an optimized bus network design in Barcelona and the existing system. The optimization of the system network design involves minimizing system costs and thereby determining optimal network layout and transit frequency. 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. Furthermore, the level of service to the user is not detrimentally affected and in fact, it is slightly improved. We therefore extrapolate and hypothesize that the optimization of transit networks in many cities would result in significant GHG emission reductions. 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.
Highlights
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
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
We will present our findings regarding the change in both cost and GHG emissions that can result when optimizing a transit network
Summary
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. This model is utilized by Estrada et al (2011) in order to design an efficient, feasible transit network for the city of Barcelona The results of this optimization serve as the inputs for our cost and GHG emission analysis that is presented . The full mathematical program and Continuum approximation methods have been developed and utilized in order to optimize transit networks with the objective of minimizing user and agency costs. In the first set of brackets of the objective function are the agency costs, comprising vehicle-km/h traveled V, the maximum number of buses required in the fleet during peak hours M, and the one-way infrastructure length L Each of these components are multiplied by a corresponding factor πi that ensures the objective function is in units of time and utilizes proper wage rates. The following section discusses how these values were utilized in a case study design and compares the total costs and GHG emissions between the current system and the proposed design
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