published journal article
conference paper
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
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.
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
book/book chapter
published journal article
We consider the dynamic traveling repair problem in which requests with deadlines arrive through time on points in a metric space. Servers move from point to point at constant speed. The goal is to plan the motion of servers so that the maximum number of requests are met by their deadline. We consider a restricted version of the problem in which there is a single server and the length of time between the arrival of a request and its deadline is constant. We give upper bounds for the competitive ratio of two very natural algorithms as well as several lower bounds for any deterministic algorithm. Most of the results in this paper are expressed as a function of β, the diameter of the metric space. In particular, we prove that the upper bound given for one of the two algorithms is within a constant factor of the best possible competitive ratio.
conference paper |
Jan 2002
Phd Dissertation |
Jun 2001
Phd Dissertation
Activity-based approaches are perhaps the most promising alternative to the current travel forecasting methodology. This dissertation first presents a pattern generation model that can serve as a link between activity and trip-based methodologies. The model uses a clustering approach to identify groups of similar activity-travel behavior and relates them to household socioeconomic attributes. Minimally, the pattern generation model is then expanded to serve as the core component of a proposed activity-based microsimulation model that constructs complete origin-destination tables using a wholly activity-based approach. The techniques developed provide due diligence to the complex nature of activity-travel behavior in terms of spatial and temporal constraints, household interactions, and the derived nature of such behavior. A successful application of the expanded model is outlined using data from the 1994 Portland activity-travel survey.