Graduation Semester and Year

2018

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Melanie L Sattler

Abstract

Against the backdrop of the increasingly complex urban passenger transportation challenges associated with megacities during the 21st century, and the effort to find the most sustainable modes of transportation for them, the spreadsheet-based model TransportLifeCAMM was developed. This model allows users in the US and Mexico to compare life cycle environmental impacts from automobile, bus, and/or subway. While other models to estimate environmental burdens from transportation exist, few of them consider emissions or energy consumption over the entire life cycle of the vehicle and the fuel (including vehicle manufacture, fuel production, maintenance, and end-of-life disposal). Furthermore, even fewer of the available models consider the infrastructure contribution to the transportation mode, and none to the level of granularity offered by TransportLifeCAMM. If the goal is to discover which is the most sustainable transportation mode, all life cycle phases for the vehicle, energy and infrastructure subsystems should be considered. The overall goal of this study was thus to develop a comprehensive life cycle assessment (LCA) spreadsheet model that compares environmental impacts of three transportation modes - subway, bus, and automobile – and their associated infrastructure, over their entire life cycle. Specific objectives were: 1. To develop a spreadsheet model for comparing life cycle impact of three transportation modes (subway, diesel bus in a Bus Rapid Transit context, and automobile), using traditional comparison criteria, 2. To apply the model to Mexico City as a case study, 3. To add an exergetic life cycle assessment to the spreadsheet model, and apply it to the case study of Mexico City as well, 4. To identify a range of impacts for the case study due to sensitivity in model inputs. The main contribution of this study was the development of a robust LCA-based methodology to evaluate and compare the environmental impacts of three transportation modes, applicable to any major city in North America. Furthermore, this methodology provided the basis and framework for TransportLifeCAMM, a freely-available, spreadsheet-based model. Since running Simapro or any other LCA software is time-consuming and complex, and requires considerable training and time to collect input data for hundreds of parameters, the user-friendly TransportLifeCAMM, based on Simapro output, allows anyone with basic spreadsheet knowledge to estimate emissions, with only a few readily-available input parameters. TransportLifeCAMM provides the measurement and analysis of environmental impacts for greenhouse gases (GHG), criteria air pollutants (CAP), cumulative energy demand and cumulative exergy demand throughout the life-cycle of each vehicle, and in units of grams of impact/passenger-kilometer. Additionally, it must be noted that no other scientific analysis or environmental/transportation study in Mexico City had been performed within an LCA framework previously to this work. Moreover, few other transportation LCA studies include the system’s infrastructure, and none to the level of granularity provided by TransportLifeCAMM. Further contributions of this research are that no LCA study has been performed across these three transportation modes in any city, and that no other LCA-based model offers an exergy analysis for transportation modes. For the LCA simulations, the Simapro version 8.3.2 software was used, and the NIST’s BEES+ method was used to conduct the main environmental impact assessment portion of the LCAs, which was supplemented by the Cumulative Energy Demand and Cumulative Exergy Demand methods for all three transportation modes. Data sources included published scientific papers and journals, governmental reports and statistics, both for the United States and for Mexico, theses and dissertations, environmental product declarations, technical specifications from the vehicles’ manufacturers, transit authority reports, public information requests, USLCI database records for the onroad vehicles, as well as Ecoinvent and other databases contained in Simapro, trade journals, engineering reference books and textbooks, industry websites, technical and operational manuals, particularly for the bus and the subway, and as of yet unpublished data from the 2017 Origin-Destination survey in Mexico City. Regarding the results of the LCAs applied to the case study of Mexico City, for the diesel bus (in the BRT system), it was found that the vehicle (bus) subsystem was the greatest contributor to the inventory for all criteria pollutants and greenhouse gases. Furthermore, it was also always the greatest contributor to the impacts, when evaluated by all impact assessment methods (BEES+, Traci, Impact 2002+, CED and CExD). For the private car, the vehicle subsystem was also the greatest contributor to both the inventory and the impacts. As expected, the car was the most environmentally burdensome system. Results also ratified previous claims of the importance of including the infrastructure for a true LCA-oriented perspective of the system under study. The main conclusion for the subway system is the acceptance of the initial hypothesis, and the rejection of the null hypothesis: the subway does represent the least environmentally burdensome transportation alternative, among the three modes studied herein. Moreover, for the subway, it was confirmed how dependent its environmental profile (i.e., its final output) is to the composition of the electricity mix. Additionally, it was found that emissions from the subway are almost entirely dependent on the electricity used for its operation, with much less significant contributions from the infrastructure subsystem than for the onroad modes. In a three-way sensitivity analysis among the three transportation modes that evaluated both environmental impacts (with the BEES+ method), the Cumulative Energy Demand and the Cumulative Exergy Demand, it was confirmed that the heavy metro or subway has the least environmental impact and energy consumption, in a per passenger-kilometer basis. This is mostly the result of an increased ridership, with the subway’s trains ability to transport a number of passengers, over their lifetime, that is at least two orders of magnitude above that of buses and cars. One of the findings of this research is that the increased lifetime performance, i.e., the greater number of kilometers travelled by each vehicle (car, bus, train) over their respective lifetimes, is also one of the factors that contributes to the subway’s lesser environmental impact over the other two transportation modes analyzed herein. In a two-way sensitivity analysis between the two mass transit modes, the bus and the subway, the low ridership case for the subway (918 passengers) was compared against both cases of “peak” buses for the BRT: the articulated bus carrying 160 passengers, and the bi-articulated bus with 240 passengers. Results showed that while the subway maintained its environmental advantage, in impacts measured in a per passenger-kilometer basis, over the articulated bus, it did not do so when compared to the bi-articulated bus, which performed marginally better than the subway. This result confirms the sensitivity of this methodology and of all transportation modes to ridership, and suggests that when planning a public transportation option, it behooves policy makers to strive to have the best available data on ridership, so as to make the best possible decision regarding on which transportation mode to invest, or to encourage.

Keywords

LCA, Subway, Heavy metro, BRT, Exergy, Mexico City, Cumulative exergy demand, BEES+

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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