research report

Public Transportation, Transportation Network Companies (TNCs), and Active Modes

published journal article

An L.A. story: The impact of housing costs on commuting

Abstract

The empirical impact of housing costs on commuting is still relatively poorly understood. This impact is especially salient in California given the state’s notoriously high housing costs, which have forced many lower- and middle-class households to move inland in search of affordable housing at the cost of longer commutes. To investigate this linkage, we relied on Generalized Structural Equation Modeling and analyzed 2012 CHTS data for Los Angeles County – the most populous county in the U.S. Our model, which jointly explains commuting distance and time, accounts for residential self-selection and car use endogeneity, while controlling for household characteristics and land use around residences and workplaces. We find that households who can afford more expensive neighborhoods have shorter commute distances (−2.3% and − 3.1% per additional $100 k to median home values around workplaces and residences respectively). Job density, distance to the CBD, and land-use diversity around workplaces have a relatively greater impact on commuting than the corresponding variables around commuters’ residences. Compared to non-Hispanics, Hispanic workers commute longer distances (+3.5%), and so do African American (+5.1%) and Asian (+2.0%) workers compared to Caucasians, while college educated workers have shorter (−2.6% to −3.6%) commutes. Furthermore, commuters in the top income brackets tend to have faster commutes than lower income workers. Finally, women’s commutes are ~41% shorter than men’s, possibly because they are balancing work with domestic responsibilities. Better understanding the determinants of commuting is critical to inform housing and transportation policy, improve the health of commuters, reduce air pollution, and achieve climate goals.

policy brief

Impacts of connected and autonomous vehicles on the performance of signalized networks: A network fundamental diagram approach

research report

Impacts of connected and autonomous vehicles on the performance of signalized networks: A network fundamental diagram approach

published journal article

Deep Ensemble Neural Network Approach for Federal Highway Administration Axle-Based Vehicle Classification Using Advanced Single Inductive Loops

Abstract

The Federal Highway Administration (FHWA) vehicle classification scheme is designed to serve various transportation needs such as pavement design, emission estimation, and transportation planning. Many transportation agencies rely on Weigh-In-Motion and Automatic Vehicle Classification sites to collect these essential vehicle classification counts. However, the spatial coverage of these detection sites across the highway network is limited by high installation and maintenance costs. One cost-effective approach has been the use of single inductive loop sensors as an alternative to obtaining FHWA vehicle classification data. However, most data sets used to develop such models are skewed since many classes associated with larger truck configurations are less commonly observed in the roadway network. This makes it more difficult to accurately classify under-represented classes, even though many of these minority classes may have disproportionately adverse effects on pavement infrastructure and the environment. Therefore, previous models have been unable to adequately classify under-represented classes, and the overall performance of the models is often masked by excellent classification accuracy of majority classes, such as passenger vehicles and five-axle tractor-trailers. To resolve the challenge of imbalanced data sets in the FHWA vehicle classification, this paper constructed a bootstrap aggregating deep neural network model on a truck-focused data set using single inductive loop signatures. The proposed method significantly improved the model performance on several truck classes, especially minority classes such as Classes 7 and 11 which were overlooked in previous research. The model was tested on a distinct data set obtained from four spatially independent sites and achieved an accuracy of 0.87 and an average F1 score of 0.72.

published journal article

Gender differences in elderly mobility in the United States

Abstract

Mobility is a critical element of one’s quality of life regardless of one’s age. Although the challenges for women are more significant than those for men as they age, far less is known about the gender differences in mobility patterns of older adults, especially in the United States (US) context. This paper reports on a study that examined potential gender gaps in mobility patterns of older adults (aged 65 years and over) in the US by analyzing data from the 2017 National Household Travel Survey. Elderly respondents were first classified into one of six clusters based on socio-demographic variables. A Structural Equation Model (SEM) was then estimated and showed that gender gaps existed in the mobility patterns of the elderly, and the differences were diverse across the different clusters. The most substantial gender gap was found in the Senior Elder with Medical Condition(s) cluster, followed by the High-income Workers cluster and the Middle-income Urban Residents cluster. In contrast, females in the Low-Income Single Elder cluster enjoyed statistically significant positive mobility differences with their male counterparts. Our results also found that female elderly in the Senior Elder with Medical Condition(s) and the Low-income Family Elder clusters suffered most after the cessation of driving, with the largest mobility gender gap in the Middle-income Urban Resident cluster. This study will help transportation planners and policymakers understand gender and other socio-demographic differences in elderly mobility. Thus, it will facilitate the development of measures to improve elderly mobility and reduce gender gaps by recognizing and addressing specific target groups’ mobility characteristics and needs rather than treating the elderly as a single potential user group.

Phd Dissertation

Research universities as gateways: The expanding roles of higher education institutions and their contribution to economic development

Publication Date

September 30, 2021

Author(s)

Areas of Expertise

Abstract

The past 30 years have witnessed a gradual expansion in the missions of many universities, and in the ways in which they contribute to local and regional economic development. While teaching and research continue to serve as the foundational core of most university missions, increased attention has been afforded to how universities, by their presence and functions, influence the spatial geographies of neighborhoods, cities, and regions. This dissertation research explores the changing roles of research universities in small and medium-sized metropolitan areas with an emphasis on their impacts across the different geographical scales by investigating associations between university presence and (1) growth in foreign-born populations; (2) the attraction and retention of highly educated residents; and (3) student-driven neighborhood change dynamics.

The findings of this dissertation extend previous studies emphasizing the increasing importance of higher education institutions to economic development activities at various scales. Results from metropolitan area level analyses demonstrate that counties with large research universities were associated with an increase in foreign-born residents following the 1990 Immigration and Naturalization Act, as well as an increase in highly educated residents in the 2000-2014 period. More specifically, while findings revealed that the presence of research universities generate significant spatial spillovers of highly educated residents from university host counties to metropolitan levels, there was little evidence of such spatially-explicit dynamics occurring amongst foreign-born residents. Furthermore, findings from neighborhood-level analyses indicated that proximity to large research university campuses may play an outsized role on the likelihood of neighborhoods undergoing studentification (i.e., student-driven neighborhood change) in the 2000-2014 period. These results may be indicative of a bifurcation of neighborhoods in university-dominant counties into wealthy and highly educated renter populations situated near the university campus, and relatively less wealthy and less educated homeowners residing on the further away from the campus or on the periphery of the county.

By exploring university contributions beyond the spheres of research, teaching, and service contributions, this dissertation presents scholars, urban planners, and policymakers with a more comprehensive portrait of the relationship between universities and their host communities. The evidence of this work suggests that the evolving role of higher education institutions, including their role as gateways for new populations, should be reflected in policymaking which seeks to leverage the locational advantages of research universities for city building or revitalization efforts. Further, policymakers and planners should also be cognizant that scale matters when considering how higher education institutions can better serve their surrounding communities. The contributions of research universities should not be thought of as monolithic or uniform, but should rather be seen as presenting different opportunities and challenges at different geographical levels.

research report

Investigation of Truck Data Collection using LiDAR Sensing Technology along Rural Highways

Phd Dissertation

Planning and Operation of a Crowdsourced Package Delivery System: Models, Algorithms and Applications

Publication Date

September 15, 2021

Author(s)

Abstract

Online shopping has increased steadily over the past decade that has led to a dramatic increase in the demand for urban package deliveries. Crowdsourced delivery, or crowd shipping, has been proposed and implemented by logistics companies in response to the growth in package delivery business. Crowdsourced delivery is a delivery service in which logistics service providers contract delivery services from the public (i.e., non-employees), instead of providing delivery services exclusively with an in-house logistics workforce. This dissertation studies different types of urban last-mile crowdsourced delivery services and provides a taxonomy for crowdsourced package delivery. Urban package crowdsourced delivery can be categorized in terms of the way packages are delivered and the role/tasks of crowdsourced drivers. Given these two dimensions, this study identifies three types of urban package crowdsourced delivery, namely, crowdsourced time-based delivery, crowdsourced trip-based delivery, and crowdsourced shared-trip delivery. Crowdsourced time-based delivery drivers are paid for their idle time and work as sub-contractors. Crowdsourced trip-based delivery matches drivers with individual tasks and utilizes the drivers for specific delivery trips. The last type, crowdsourced shared-trip delivery utilizes the common segments of a crowdsourced personal vehicle trip to deliver packages. In this type, the package shares part of the driver trip. The literature formulates the crowdsourced delivery problem as a Vehicle Routing Problem (VRP) and proposes a variety of solution approaches. However, all the solution algorithms are limited to relatively small-scale problems. In addition, the factors that impact the efficiency and effectiveness of crowdsourced delivery have not been thoroughly analyzed. To bridge the gap in crowdsourced delivery and urban freight logistics, this dissertation provides an alternative formulation for the static crowdsourced shared-trip delivery problem and proposes a novel decomposition heuristic to solve the problem. The alternative formulation is based on the set partitioning problem. The novel decomposition heuristic handles packages that are served by shared personal vehicles (SPVs) and dedicated vehicles (DVs), separately. After that, the algorithm deploys a package switch procedure, which rearranges packages between SPVs and DVs. The dissertation discusses various algorithms employed to solve different sub-problems, such as the budgeted k-shortest path, large scale bi-partite matching, decision of package switching and vehicle routing. To validate the models and algorithms, this dissertation presents a numerical case study that uses the network of the City of Irvine, CA, USA. The results of the numerical study unveil interesting results that are valuable to both researchers and industrial practitioners. The results indicate that crowdsourced shared-trip delivery service can reduce total cost by between 20% to 50%, compared to a delivery service that exclusively uses its own dedicated vehicles and drivers. However, the results show that dedicated vehicles are still required since the shared vehicles are not able to serve all packages even with a considerably large set of candidate shared vehicles. Vehicle Miles Traveled (VMT) savings depend on the crowdsourced driver selection and their trip origins. The dissertation also analyzes and discusses important factors that impact the effectiveness of crowdsourced delivery. In particular, the dissertation includes sensitivity analysis results with respect to changes in the depot location and the willingness of shared vehicles to detour.

Phd Dissertation

Developing Demand Model for Commuter Rail while Analyzing Underlying Attitudes of the System

Abstract

There have been laws passed in California (SB32) that would require the State to cut its Greenhouse Gas Emissions (GHG) to 40% of 1990 levels by 2030 to combat climate change. With cars contributing to 43% of GHG emissions in California to reach that goal there will need to be a significant reduction in Vehicle Miles Travelled (VMT). A way to quickly reduce VMT is to invest in existing rail systems specifically commuter rails. An investigation was conducted to model the potential effects of improving commuter rail services on a state vs. national level, station-by-station level, and a regional level. To conduct the research data was gathered from the National Transit Database, Longitudinal Employer-Household Dynamics site, and the Environmental Protection Agencies Smart Location Database (EPA-SLD) for the year 2014. The California Model unlinked passenger trips are more sensitive to the hours of service than the National Model. Also, the California Model is more sensitive to log peak vehicles operated which would imply that the more vehicles or frequency of the vehicles servicing people can have a large impact on passenger trips. The Station boarding and egress models were the best when there were exogenous latent variables in the regression model. The latent variables Mixed-Use Density and Work Opportunity play a significant role in transit boardings and egress by stating that if the mixed-use density increases the employment, employment entropy, and ratio of jobs accessible in 45 minutes increases. Model 2 is superior of the SEM models created. The ridership factors that the passenger rates to all the observed variables and the measure of their satisfaction with the variables can be a tool to use for improving service quality and for planning for future services. In the long run, this could have cost savings because if there is information about the riders’ preferences there can be improvements made specific to what is valued as important. This model can be easily modified to fit other transit services in many different regions or countries because of the framework structure which can be used for analyzing any type of service from survey responses.