journal article preprint

Impacts of the COVID-19 Pandemic on Telecommuting and Travel

Abstract

This chapter examines changes in telecommuting and the resulting activity-travel behavior during the COVID-19 pandemic, with a particular focus on California. A geographical approach was taken to “zoom in” to the county level and to major regions in California and to “zoom out” to comparable states (New York, Texas, Florida). Nearly one-third of the domestic workforce worked from home during the pandemic, a rate almost six times higher than the pre-pandemic level. At least one member from 35 percent of U.S. households replaced in-person work with telework; these individuals tended to belong to higher-income, White, and Asian households. Workplace visits have continued to remain below pre-pandemic levels, but visits to non-work locations initially declined but gradually increased over the first nine months of the pandemic. During this period, the total number of trips in all distance categories except long-distance travel decreased considerably. Among the selected states, California experienced a higher reduction in both work and non-workplace visits, and the State’s urban counties had higher reductions in workplace visits than rural counties. The findings of this study provide insights to improve our understanding of the impact of telecommuting on travel behavior during the pandemic

published journal article

Health and equity impacts from electrifying drayage trucks

Abstract

Diesel heavy-duty drayage trucks (HDDTs) serving the Ports of Los Angeles and Long Beach in Southern California are large contributors to regional air pollution, but cost remains an obstacle to replacing them with zero-emission HDDTs. To quantify the health and equity impacts of operating diesel HDDTs, we built a microscopic simulation model of a regional freeway network and quantified their emissions of PM2.5 (particulate matter with a diameter < 2.5 μm) and CO2 in 2012 and 2035, before estimating their contribution to selected health outcomes. We found that 483 premature deaths ($5.59 billion) and 15,468 asthma attacks could be attributed to HDDTs in 2012. Regulations and technological advances could shrink these impacts to 106 premature deaths ($1.31 billion) and 2,142 asthma attacks in 2035 (over 2/3 accruing to disadvantaged communities) despite population growth and a 145 % jump in drayage traffic, but they still justify replacing diesel HDDTs with zero-emission HDDTs by 2035.

book/book chapter

Understanding and Modeling the Impacts of COVID-19 on Freight Trucking Activity

Abstract

Restrictions on travel and in-person commercial activities in many countries (e.g., the United States, China, European countries, etc.) due to the global outbreak and rapid spread of the coronavirus disease 2019 (COVID-19) have severely impacted the global supply chain and subsequently affected freight transportation and logistics. This chapter summarizes the findings from the analysis of truck axle and weight data from existing highway detector infrastructure to investigate the impacts of COVID-19 on freight trucking activity. Three aspects of COVID-19 truck impacts were explored: drayage, long and short-haul movements, and payload characteristics. This analysis revealed disparate impacts of this pandemic on freight trucking activity because of local and foreign policies, supply chain bottlenecks, and dynamic changes in consumer behavior. Due to the ongoing effects of COVID-19, it is not yet possible to distinguish between transient and long-term impacts on freight trucking activity. Nonetheless, a future expansion of the study area and the incorporation of other complementary data sources may provide further insights into the pandemic’s impacts on freight movement.

Phd Dissertation

Alternative Fuel Adoption Behavior of Heavy-duty Vehicle Fleets

Abstract

Alternative fuel adoption by heavy-duty vehicle (HDV) fleets can bring substantial benefits to both current local communities and future generations by reducing air pollutants and greenhouse gas emissions. However, the penetration rate of alternative fuel vehicles (AFVs) is still very low in the HDV sector. Revealing HDV fleet operator perspectives towards alternative fuels can serve as the basis for developing effective policies for accelerating the diffusion of these technologies. This dissertation aims to fill a key knowledge gap, where such fleet operator perspectives have rarely been addressed, by exploring alternative fuel adoption behavior of HDV fleets.An initial theoretical framework was first developed based upon existing theories and literature to conceptually understand AFV fleet adoption behavior in organizations. This initial framework consists of a five-stage adoption process as well as two levels of sub-frameworks: at the decision-making unit level and the individual (e.g., vehicle drivers) acceptance level. Next, it was attempted to empirically improve the initial framework by investigating 20 organizations operating HDVs in the State of California via in-depth qualitative interviews and project reports. A total of 29 adoption and 42 non-adoption cases was probed across various alternative fuel technologies, including natural gas, propane, electricity, hydrogen, biodiesel, and renewable diesel options. The qualitative data was analyzed using content and thematic analyses, by which numerous themes and hypotheses were developed to build a theory explaining heavy-duty AFV fleet adoption behavior. Based on these qualitative inferences, a conceptual modelling framework was proposed for estimating demand for heavy-duty AFVs under different policy and technology advancement scenarios. An overall structure along with specific modules and components for this framework are presented. As an ongoing work, a stated preference choice experiment was designed to quantitatively operationalize one of the modules, to estimate AFV choice probabilities. The feasibility of this modelling approach is proposed to be examined in a case study interviewing California drayage fleet operators. Finally, the research findings contribute theoretically and empirically to a better understanding of the demand-side aspects of AFV adoption by HDV fleet operators, particularly in California and in the other US states that follow California’s environmental policies.

Phd Dissertation

Resilient spatiotemporal truck monitoring framework using inductive signature and 3d point cloud-based technologies

Abstract

Understanding the spatiotemporal distribution of commercial vehicles is essential for facilitating strategic pavement design, freight planning, and policy making. Hence, analysts and researchers have been increasingly interested in collecting more diverse high granularity truck data across different truck characterization schemes to meet these various needs across the roadway network to better understand their distinct operational characteristics and dissimilar impacts on infrastructure and the environment. Existing truck monitoring infrastructure is limited in spatial coverage across the roadway network due to high installation and maintenance costs. The recently developed Truck Activity Monitoring System (TAMS) by the University of California Irvine Institute of Transportation Studies provides a cost-effective solution for monitoring truck movements statewide across California along major freeways networks through existing inductive loop infrastructure enhanced with inductive signature technology. Nonetheless, it possesses three major limitations: model bias against underrepresented truck classes, spatial coverage limitation on rural highways, and system obsolescence over time. This dissertation explored a resilient spatiotemporal truck monitoring system using inductive loop signature and multi-array Light Detection and Ranging (LiDAR) sensor technologies to address the aforementioned issues and to improve truck monitoring capabilities across the roadway network. The designed system comprises three major parts: Inductive loop sensors for major highway truck monitoring, multi-array LiDAR sensors for rural highway truck monitoring, and a self-learning truck classification framework through a sensor integration framework. The first part of the system was built upon the existing Truck Activity Monitoring System (TAMS) developed by ITS Irvine and addresses prediction model biasness caused by inherently imbalanced truck datasets to provide reliable truck speed estimation and truck classification data. The second part explored non-intrusive LiDAR-based sensing technologies to fill the surveillance gap along rural highway corridors. This section developed a truck classification method using a LiDAR sensor oriented to provide a wide field-of-view of roadways. Finally, a self-learning framework for truck classification systems was designed to address system obsolescence through the integration of inductive loop sensors and LiDAR sensors, the latter of which has been proven in this dissertation to have the ability to recognize truck axle configuration. This framework enhances the resilience of the signature-based FHWA classification model with an intelligent system update to accommodate the change of the truck designations over time and significantly reduces the overall burden of periodic model calibration by utilizing the information stored in the legacy model. 

published journal article

Grocery shopping in California and COVID-19: Transportation, environmental justice, and policy implications

Abstract

To understand how COVID-19 changed grocery shopping and explore implications for transportation and environmental justice, we surveyed in May 2021 California members of KnowledgePanel®, the largest and oldest U.S. probability-based panel. We asked how frequently Californians grocery shopped before and during the pandemic, and how they may grocery shop afterward in-store, online with home delivery (“e-grocery”), or online with store/curbside pick-up (“click-and-pick”). We found that most Californians continued to grocery shop in-person during the pandemic, although less frequently than before. Many relied more on e-grocery (+8.9 %) and click-and-pick (+13.3 %), although older generations remained attached to in-store shopping. African American households grocery shopped in-store less than Whites pre-pandemic; post-pandemic, they may compensate with more e-grocery and click-and-pick. While higher levels of environmental injustice (based on CalEnviroScreen) were associated with less in-store shopping, we found no association with e-grocery or click-and-pick. Our results have implications for travel, food logistics, and parking management.

published journal article

Equity Implications of Robo-Taxis on Job Accessibility: Avoiding the Ecological Fallacy with Agent-Based Models

Abstract

Robo-taxis or shared-use automated vehicle-enabled mobility-on-demand services (SAMSs) are now in operation in the US and China. By removing drivers’ labor costs, SAMSs promise to provide significantly lower-cost transportation than human-driven mobility-on-demand services. Under this assumption, prior research indicates SAMS can provide sizable employment accessibility benefits to workers. The current paper aims to analyze the distribution of SAMS accessibility benefits across segments of the population (i.e., perform an equity analysis) using an agent-based travel modeling approach. The study’s methodology (i) clusters workers by their socio-demographic and -economic characteristics using latent class analysis, (ii) estimates hierarchical work location and commute mode choice models for four worker segments, and (iii) obtains logsum-based monetary measures of accessibility for each worker in a synthetic population of Southern California. Using this information, we analyze the distributions of SAMS accessibility benefits across several population segmentations. We utilize box plots to visualize the distributional differences across population segments. Additionally, we use ANOVA and post-hoc Tukey’s Honestly Significant Difference tests to analyze the overall and inter-group statistical significance of the distributional differences, respectively. The results indicate that low-income, Black, and Hispanic workers receive larger SAMS accessibility benefits on average than high-income, White, and Asian workers. Additionally, workers in zero-car households benefit more from SAMSs than one- and multi-car households, particularly after conditioning on the transit accessibility of the worker’s residence. The study also aggregates the agents into their origin census tracts, classifies the census tracts based on agent socio-demographic attributes, and then analyzes the distribution of SAMS accessibility benefits across census tract designations (e.g., low median income tracts vs. high median income tracts). The study finds that if analysts were to make individual-level inferences based on the spatial analysis, the inferences would be inaccurate in the case of household income and age, thereby misinforming policymakers regarding who benefits more/less from SAMS.

presentation

Kent Distinguished Lecture, University of Illinois Transportation Center, Nov 2022: "Data, modeling and emerging technologies on the road to sustainable freight transportation."

Phd Dissertation

PUBLIC TRANSPORTATION AT A CROSSROADS Transportation Network Companies, COVID-19, and Transit Ridership

Publication Date

August 31, 2022

Author(s)

Abstract

Public transportation in the U.S., including in California, was declining before COVID-19, and the pandemic made a bad situation much worse. In this dissertation, I analyze data from the 2009 and 2017 National Household Travel Surveys and from a California survey administered in May 2021 by IPSOS using both discrete choice (cross-nested logit and generalized ordered logit) and quasi-experimental (propensity score matching) tools first to investigate how Transportation Network Companies (TNCs, e.g., Uber and Lyft) impacted transit ridership before COVID-19, before analyzing how COVID-19 affected transit and other modes.In Chapter 2, my results for the U.S. show that individuals/households who use either public transit or TNCs share socio-economic characteristics, reside in similar areas, and differ from individuals/households who use neither public transit nor TNCs. In addition, individuals/households who use both public transit and TNCs tend to be Millennials or belong to Generation Z, with a higher income, more education, no children, and fewer vehicles than drivers.In Chapter 3, I quantify the impact of TNCs on household transit use by comparing travel for households from the 2017 NHTS (who had access to both transit and TNCs) matched with households from the 2009 NHTS (who only had access to transit) using propensity score matching. Overall, I find a 22% drop for weekdays (1.6 fewer daily transit trips by each household) and a 15% decrease for weekends (1.4 fewer daily transit trips by each household).In Chapter 4, I analyze how Californians changed transportation modes due to COVID-19 and explore their intentions to use different modes after COVID-19. I find that driving but especially transit and TNCs could see substantial drops in popularity after the pandemic. Many Hispanics, African Americans, Asians, lower-income people, and people who would like to telecommute more intend to use transit less. Key obstacles to a resurgence of transit after COVID-19 are insufficient reach and frequency, shortcomings that are especially important to younger adults, people with more education, and affluent households (“choice riders”).My findings highlight the danger of public transit entering into outsourcing agreements with TNCs, neglecting captive riders, and exposing choice riders to TNCs.

Phd Dissertation

Matching Mechanisms for social good: case studies in transport congestion, low-income housing, and food surplus redistribution

Publication Date

July 31, 2022

Author(s)

Abstract

For several decades now, matching mechanisms have been deployed, sometimes implicitly, to solve economic and social problems with unprecedented efficiency. Most notably, the kidney transplant matching algorithm has been key in saving many lives, 39,000 donation in 2019 alone. Likewise, the National Residency Matching Program successfully employed in the United States today uses a matching mechanism that places medical students into hospital residencies. A similar mechanism is used in college and public school admissions around the United States, most famously, in the Boston and New York City. This dissertation will continue this long history of applying matching mechanisms towards efficiently solving social problems.

We begin with a summary of relevant definitions and other terminology in chapter1, all of which will be applied in the chapters that follow. Chapter 2 will examine two concurrent social problems, over-production of resources that contributes to global waste, and lack of access to wasted resources by people living on the economic margin. We will contrast two possible solutions to both problems, that is, a decentralized vs a centralized matching solution. The feasibility of both solutions will be tested through theoretical investigation and two qualitative case studies in food surplus redistribution in the United Kingdom and allocation of housing to unhoused household in Los Angeles County during the pandemic.

Chapter 3 will give a more detail examination of allocation of housing to the unhoused by examining the efficiency and robustness to manipulation of the algorithm that was employed by LA county vs a centralized matching mechanism. Whereas Chapter 4 will explore an online matching mechanism solution to the problem of traffic congestion pricing. The proposed solution combines a matching algorithm, which assigns drivers to routes at the time of travel, with an anticipatory pricing mechanism that determines how much each traveling driver pays if they choose to use a congested route.

The conclusion will present open problems implied in the preceding three chapters.