conference paper
published journal article
While urban poverty has been known to be spatially concentrated in inner-city areas for a long time, the degree of poverty concentration has declined substantially since the 1990s, whereas poverty has increasingly expanded to suburban areas to which relatively little attention has been paid. This study examines how poverty distribution has changed in the Los Angeles-Long Beach Combined Statistical Area and why. More specifically, an investigation is made to capture the detailed changes of poverty rates in over three thousand census tracts over the last two decades and to identify driving forces behind these spatiotemporal changes by employing spatial regression models. Results show that high poverty areas have stretched over space, not in a way that expands their overall size but in a way that increases the degree of spatial fragmentation throughout the last two decades. The results also reveal that neighborhood poverty change is largely shaped by wealth clustering and other spatially-explicit processes.
conference paper
published journal article
published journal article
Computational efficiency and first in, first out (FIFO) are both important issues in applications such as dynamic traffic assignment. This paper first shows by example the FIFO properties of a computationally efficient commodity-based kinematic wave (CKW) model of network traffic flow. After the development of measurements of FIFO violation among commodities in location and time on the basis of the misplacement of vehicles in total and commodity traffic, it is argued theoretically that numerical CKW solutions converge to FIFO ones. Then, with numerical examples, it is shown that FIFO violation in CKW solutions is a function of the simulation time and the number of commodities but decreases with decreasing cell lengths, even for infinite number of commodities. Finally, the possible implications of this study are discussed.
working paper
The history of demand modeling for person travel has been dominated by the modeling approach that has come to be referred to as the four step model (FSM) (see Chapter 2). Travel, always viewed in theory as derived from the demand for activity participation, in practice has been modeled with trip-based rather than activity-based methods (as presented in Chapter 4). Trip origin-destination (O-D) rather than activity surveys form the principle database. The influence of activity characteristics decreases, and that of trip characteristics increases, as the conventional forecasting sequence proceeds. The application of this modeling approach is near universal, as in large measure are its criticisms (these inadequacies are well documented, e.g., by McNally and Recker (1986)). The current FSM might best be viewed in two stages. In the first stage, various characteristics of the traveler and the land use – activity system (and to a varying degree, the transportation system) are “evaluated, calibrated, and validated” to produce a non-equilibrated measure of travel demand (or trip tables). In the second stage, this demand is loaded onto the transportation network in a process than amounts to formal equilibration of route choice only, not of other choice dimensions such as destination, mode, time-of-day, or whether to travel at all (feedback to prior stages has often been introduced, but not in a consistent and convergent manner). Although this approach has been moderately successful in the aggregate, it has failed to perform in most relevant policy tests, whether on the demand or supply side.
policy brief
Between 2014 and 2017, transit ridership in the U.S. declined by 6%, while bus transit ridership fell by 9.5%. Some regional agencies such as the Orange County Transportation Authority (OCTA) were particularly affected. Changing socioeconomic conditions, service quality, and increased competition from transportation network companies (e.g., Uber, Lyft) are some of the reasons behind the observed decline in bus ridership. The implementation of The Safe and Responsible Drivers Act of 2013 (Assembly Bill 60) may have also impacted ridership, which directs the California Department of Motor Vehicles to issue a driver’s license to applicants who are unable to provide proof of legal presence in the United States but can provide satisfactory proof of identity as well as California residency. Some of these individuals could have been relying on transit since they could not legally obtain a driver’s license. UC Irvine researchers examined if observed line-level changes in OCTA bus boardings could be partly attributed to AB 60, while controlling for differences in transit supply, socioeconomic variables, gas prices, and the built environment. Using fixed effects panel data models, the team analyzed monthly boardings on different OCTA route classifications—local, community, Express, and station link routes—one year before (2014) and two years after (2015 and 2016) AB 60’s implementation.
research report |
Aug 2025
conference paper
research report
The overall objective of this project is to develop an optimal resource allocation tool for the entire state of California using Geographic Information Systems and widely available data sources. As this tool evolves it will be used to make investment decisions in transportation infrastructure while accounting for their spatial and social distribution of impacts. Tools of this type do not exist due to lack of suitable planning support tools, lack of efforts in assembling data and information from a variety of sources, and lack of coordination in assembling the data. Suitable planning support tools can be created with analytical experimentation to identify the best methods and the first steps are taken in this project. Assembly of widely available data is also demonstrated in this project. Coordination of fragmented jurisdictions remains an elusive task that is left outside the project. When this project begun we confronted some of these issues and embarked in a path of feasibility demonstration in the form of a pilot project that gave us very encouraging results. In spite of this pilot nature aiming at demonstration of technical feasibility, substantive conclusions and findings are also extracted from each analytical step.In this project we have two parallel analytical tracks that are a statewide macroanalysis (called the zonal based approach herein) and an individual and household based microanalysis (called the person based approach herein). In the statewide macroanalysis we study efficiency and equity in resource allocation. Resources are intended as infrastructure availability and access to activity participation offered by the combined effect of transportation infrastructure and land use measured by indicators of accessibility. Stochastic frontiers are used to study efficiency and a particular type of inequality measurement called the Theil fractal inequality index is used to study equity in the macroanalysis. The outcome of this analysis are maps identifying places in California that enjoy higher levels of service when compared to the entire state and places which succeeded in allocating resources in a relatively better way than others. In the individual microanalysis we use the accessibility indicators from the macronalysis and expand them by defining a new set of indicators at a second level of spatial (dis)aggregation. Then we use them as explanatory factors of travel behavior with focus on the use of different travel models (e.g., driving alone, use of public transportation and so forth). As expected infrastructure availability and accessibility to activity opportunities has a significant and substantive effect on the use of different modes. Many resource allocation decisions, then, will impact behavior, which in turn influences the optimality and equity conditions. This implies that decisions about where and when to allocate resources in public and private transportation needs to account for changes in behavior in a dynamic fashion, using scenarios of accessibility provision and assessing their impact by studying activity and travel behavior changes.
published journal article