published journal article
published journal article
The complex urban life has prompted commuters to combine non-work activities with their work trips to save time and money, resulting in commute-based trip chains closely tied to mode choice. Dhaka, one of the world’s most densely populated megacities and the capital of Bangladesh, exhibits the potential for unique trip chaining patterns driven by its complex land use and extensive range of transport options. This study examines the trip chaining behavior of commuters in Dhaka, utilizing Latent Class Analysis (LCA) to categorize them based on their trip chaining and mode use characteristics. The analysis reveals four distinct commuter classes. Class 1 represents simple trip chain makers, traveling without additional stops between home and work, using motorized transport. They typically belong to middle- to high-income households with access to private vehicles. Class 2 is characterized by complex trip chain makers – individuals who combine work and non-work activities – primarily during the journey to home, utilizing motorized vehicles. Females and those from middle- to high-income households tend to fall into this group. Class 3 consists of simple trip chain makers who rely on public transit or non-motorized vehicles. These commuters are mainly low-income males without access to private vehicles. Finally, Class 4 represents complex trip chain makers using non-motorized transport and typically belong to middle-income households with no private vehicle access. The findings offer valuable insights into the complex travel behavior of commuters, aiding the development of effective travel demand management policies, particularly in addressing peak-hour traffic contributed by commuters.
MS Thesis
Most existing traffic flow models rely on data collection methods that require a detailed layout of networks with compilations of recorded individual trip data. Although these procedures have been reliable, they also possess disadvantages such as high computation costs and a lack of privacy protection. Thus, in search of a lower cost alternative that can also effectively protect consumer privacy, we analyzed the Bathtub traffic flow model as a potentially viable data collection protocol.To test whether concepts can be proven, conservation equations can be consistent, and outputs can be obtained with accuracy through the Bathtub model, I performed model calibration and validation on data provided by Bluebikes, Metro Boston’s public bike share program. The following components were tested: unified relative space paradigm, conservation equations, and Bathtub model. These components were tested through the following steps: data organization, definition of steps, Bathtub model selection, Bathtub variables, Bathtub relative variables, average speed, conservation equation validation, and model solution. The unified relative space paradigm unified the network trips using remaining trip distances. Bluebikes trip distance distribution showed a log-normal distribution, which failed to meet the negative exponential and time-independent trip distance distribution assumption. The conservation in total trips equation was validated with perfect accuracy, while the conservation in trip-miles-traveled equation was validated with good accuracy. The generalized Bathtub model solution also produced accurate results, where space-mean speed yielded the best results. Given the model’s novelty and potential for privacy-preservation and application, there are many possibilities for future study, such as: data collection protocols with the Bathtub model, compatibility with other transportation modes, and comparisons with reality. This study establishes the preliminary step in putting theory to practice, as we aim towards application.
MS Thesis
Vehicle dismantling facilities play a critical role in recycling metals from end-of-life vehicles (ELVs). However, these facilities can impose environmental burdens on nearby communities, including noise, air pollution, and groundwater contamination, especially when operations do not comply with legal standards. While the siting of hazardous facilities has been widely studied through an environmental justice (EJ) lens, vehicle dismantlers have received limited attention. This study examines these patterns in California, highlighting their unique characteristics and implications for social and environmental equity. Using a Heteroskedastic Binary Logit model to capture local differences, this thesis shows that vehicle dismantlers are more likely to be located in census tracts with higher levels of social disadvantage, although not disproportionately in low-income areas. Composite variables, such as the CalEnviroScreen score and components of the Social Vulnerability Index, are important for predicting the presence of dismantlers, linking these facilities to broader patterns of environmental and social vulnerability. While results do not explicitly find racial disparities, findings suggest that vehicle dismantlers are concentrated in highly polluted areas, which are often disproportionately inhabited by disadvantaged populations, which raises environmental injustice concerns. Conversely, population density is also a significant factor, which is inversely correlated with the presence of vehicle dismantlers. These facilities often require substantial land, which is expensive in densely populated urban areas. A better understanding of the factors influencing the siting of these facilities is useful to craft better policies to address social and environmental injustices, promote sustainability and enhance social equity.
conference paper
published journal article
Soil-based risk assessment shows a U.S. city to exceed federal acceptable risk levels for both non-carcinogenic and carcinogenic health outcomes in many areas, with total risk and soil contamination being correlated with socioeconomic factors. , (1) Background: exposure to heavy metals is associated with adverse health effects and disproportionately impacts low-income communities and communities of color. We carried out a community-based participatory research study to examine the distribution of heavy metal concentrations in the soil and social vulnerabilities to soil heavy metal exposures across Census tracts in Santa Ana, CA. (2) Methods: soil samples ( n = 1528) of eight heavy metals including lead (Pb), arsenic (As), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), cadmium (Cd), and zinc (Zn) were collected in 2018 across Santa Ana, CA, at a high spatial resolution and analyzed using XRF analysis. Metal concentrations were mapped out and American Community Survey data was utilized to assess metals throughout Census tracts in terms of social and economic variables. Risk assessment was conducted to evaluate carcinogenic and non-carcinogenic risk. (3) Results: concentrations of soil metals varied according to landuse type and socioeconomic factors. Census tracts where the median household income was under $50 000 had 390%, 92.9%, 56.6%, and 54.3% higher Pb, Zn, Cd, and As concentrations compared to high-income counterparts. All Census tracts in Santa Ana showed hazard index >1, implying the potential for non-carcinogenic health effects, and nearly all Census tracts showed a cancer risk above 10 −4 , implying a greater than acceptable risk. Risk was predominantly driven by childhood exposure. (4) Conclusions: findings inform initiatives related to environmental justice and highlight subpopulations at elevated risk of heavy metal exposure, in turn underscoring the need for community-driven recommendations for policies and other actions to remediate soil contamination and protect the health of residents.
policy brief
In December 2018, the California Air Resources Board (CARB) approved the Innovative Clean Transit regulation, which is designed to transition the state to all-electric bus fleets by 2040. To comply with this first-of its-kind regulation, transit agencies have two alternatives: battery electric buses (BEBs) and hydrogen fuel cell electric buses (FCEBs). These options vary in energy requirements, overall effectiveness in reducing different emission types, associated life cycle costs (including disposal of the bus), and ability to meet operating needs of transit agencies. To support transit agencies and decision makers transition to cleaner bus technologies, researchers at UC Irvine developed a life cycle-based analysis (LCA) tool to estimate the potential costs and benefits of switching to BEBs and FCEBs compared to conventional buses. The LCA tool was tested on the Orange County Transportation Authority (OCTA) to better understand the environmental impacts and cost constraints.
published journal article
working paper
Demand for public transit services in most urban areas is increasingly concentrated in the peak period. However, peak period service is significantly more expensive to the transit agency than its other services and usually produces larger deficits. Faced with pressures to maintain or increase commuter services, yet also to control rapidly escalating deficits, transit agencies are in need of strategies which improve the cost-effectiveness of commuter transportation. Several innovative service strategies which make use of the private sector–service contracting, service turnovers, vanpooling-chave considerable potential to achieve this objective, and are alternatives to traditional transit agency approaches to problem solving.Based on a study of 8 transit agencies in 8 diverse metropolitan areas, all with some significant private sector activity in commuter transportation, this paper examines transit agency utilization of these innovative private sector strategies. It determines the reasons these agencies have or have not adopted these strategies, and identifies the major barriers to their more widespread utilization. The initial incentive to consider non-traditional approaches comes from fiscal and/or service pressures which require some change in the status quo, but whether private sector strategies are actually utilized depends largely on four factors: 1) management interest in non-traditional approaches, 2) analyses which demonstrate the utility of innovative approaches, 3) discretionary rather than dedicated local subsidies, and 4) the ability of local government officials to influence the transit agency’s service and budget decisions. The main barriers to innovation are traditional management orientation, labor constraints posed by federal legislation and/or local union contracts, and subsidy and decision making arrangements which give the agency no strong incentive to improve the cost-effectiveness of its different types of services.
published journal article