published journal article

A vehicle ownership and utilization choice model with endogenous residential density

Abstract

This paper explores the impact of residential density on households’ vehicle type and usage choices using the 2001 National Household Travel Survey (NHTS). Attempts to quantify the effect of urban form on households’ vehicle choice and utilization often encounter the problem of sample selectivity. Household characteristics that are unobservable to the researchers might determine simultaneously where to live, what vehicles to choose, and how much to drive them. Unless this simultaneity is modeled, any relationship between residential density and vehicle choice may be biased. This paper extends the Bayesian multivariate ordered probit and tobit model developed in Fang (2008) to treat local residential density as endogenous. The model includes equations for vehicle ownership and usage in terms of number of cars, number of trucks (vans, sports utility vehicles, and pickup trucks), miles traveled by cars, and miles traveled by trucks. We carry out policy simulations that show that an increase in residential density has a negligible effect on car choice and utilization, but slightly reduces truck choice and utilization. The largest impact we find is a -.4 arc elasticity of truck fuel use with respect to density. We also perform an out-of-sample forecast using a holdout sample to test the robustness of the model.

published journal article

Investigation of roadside fine particulate matter concentration surrounding major arterials in five Southern Californian cities

Abstract

The built environment surrounding arterials affects the dispersion of vehicular emissions in urban areas, modifying the potential risks to public health. In order to study the influence of urban morphometry on flow and dispersion of vehicular fine particulate matter emissions, in the summer of 2008 field measurements were performed in major arterials located in five Southern Californian cities with different building geometries. In each city, local mean wind, turbulence, virtual temperature, roadside DustTrak Fine Particles (DTFP) concentration, and traffic flow data were collected in 2-hr measurement periods during morning and evening rush hours and lighter midday traffic, over a period of 3 days. The calculated Monin–Obukhov length, L, suggests that near-neutral and slightly unstable conditions were present at both street and roof levels. The nondimensional forms of turbulent wind and temperature fluctuations show that the data at street level within the urban canopy can be represented using the Monin–Obukhov similarity theory. Generalized additive models were applied to analyze the impact of meteorological and traffic-related variables on fine particle concentrations at street level. Compared to other variables, urban-scale background concentrations were the most important variables in all five models. The results confirmed that turbulent mixing in urban areas dominated the variation of roadside particle concentrations regardless of urban geometry. The distance from the local sites to the nearby monitoring stations affected model performance when urban-scale concentrations were used to predict middle-scale concentrations by generalized additive models (GAMs). A radius of influence for background concentrations was 6–10 km. There were also relationships between concentration and other variables affecting the local components of the concentrations, such as wind direction, sensible heat flux, and vertical wind fluctuation, although the influences were much weaker.

published journal article

Fine particulate concentrations on sidewalks in five Southern California cities

Abstract

This research provides an exploratory examination of the factors associated with fine particle concentrations in intersection and sidewalk microenvironments in five study areas in the Los Angeles region. The study areas range from low-density, auto-oriented development patterns to dense urban areas with mid- and high-rise buildings. Average concentrations of FPDT (fine particle concentrations measured with DustTrak Aerosol Monitors) ranged from about 20 to 70 μg m−3 across study areas during stationary and mobile (walking) monitoring in morning, midday, and evening periods. Results suggest that fine particle concentrations are highly variable on urban sidewalks. A regression analysis shows that concentrations are associated with traffic and the proximate built environment characteristics after accounting for meteorological factors, time of day, and location in the region. Regressions show higher concentrations were associated with lower wind speeds and higher temperatures, higher adjacent passenger vehicle traffic, higher ambient concentrations, and street canyons with buildings of over five stories. Locations in street canyons with 2–5 story buildings and with more paving and open space had lower concentrations after accounting for other factors. The associations with traffic and built environment variables explained a small amount of the variation in FPDT concentrations, suggesting that future research should examine the relative role of localized traffic and built environment characteristics compared to regional ambient concentrations and meteorology.

research report

Fine Particulate Concentrations Near Arterial Streets: The Influence of Building Placement and Wind Flow

Abstract

This paper provides preliminary evidence that the placement of buildings influences the concentration of fine particulates by altering wind flow. The authors collected measurements of fine particulate concentration, wind speed, wind direction, and traffic levels around five Southern California arterials selected to represent a range of building densities. In some cases the difference in average concentrations between opposite sides of the street was on the order of 10 μg/m3. In most cases the concentration was higher on the upwind side of the street, where the wind wakes of buildings limit the dispersion of particulates. Although this work is exploratory in nature, it reveals that fine particulate concentrations can vary even within a single city block, a scale finer than those used in current policy models. Given the trend towards infill development and densification in many places, this is an important topic that warrants further research to more fully understand the influence of the built environment on air quality.

research report

An Activity-Based Assessment of the Potential Impacts of Plug-In Hybrid Electric Vehicles on Energy and Emissions Using One-Day Travel Data

Abstract

With the success of Hybrid Electric Vehicles (HEVs) in the automobile market, Plug-In Hybrid Electric Vehicles (PHEVs) are emerging as the next evolution of this attractive alternative. PHEV market penetration is expected to lead to lower gasoline consumption and less emission. The main objective of this research is to assess PHEVs’ energy profile impacts based on simulation of vehicles used in activity and travel patterns drawn from the 2000-2001 California Statewide Household Travel Survey. Simulations replicating reported continuous one day data are used to generate realistic energy impact assessment of PHEV market penetration.
A secondary objective is to estimate the decreased gasoline consumption and increased electricity demand in California. This will involve testing various scenarios involving battery charging to develop policies and strategies to mitigate the recharging demands placed on the grid during periods of peak consumption.

published journal article

Development of an Estimation Procedure for an Activity-Based Travel Demand Model

Abstract

In this article, we implement an estimation procedure for a particular mathematical programming activity-based model to estimate the relative importance of factors associated with spatial and temporal interrelationships among the out-of-home activities that motivate a household’s need or desire to travel. The method uses a genetic algorithm to estimate coefficient values of the utility function, based on a particular multidimensional sequence alignment method to deal with the nominal, discrete attributes of the activity/travel pattern (e.g., which household member performs which activity, which vehicle is used, sequencing of activities), and a time sequence alignment method to handle temporal attributes of the activity pattern (e.g., starting and ending time of each activity and/or travel). The estimation procedure is tested on data drawn from a well-known activity/travel survey.

published journal article

A mathematical programming formulation of the household activity rescheduling problem

research report

Improving the Distribution of Densities in Southern California

Abstract

Many of the biggest transportation challenges in Southern California arise not due to its overall density but due to the lack of concentration of densities. While recent years have witnessed increasing efforts to expand public transit services and encourage compact development in transit areas, there is a dearth of research providing support for improving the distribution of densities in the region. This project adopts a simultaneous equation modeling (SEM) approach to reveal the complexity of parcel-level (residential) land use intensification dynamics in a five-county Southern California metropolitan region with emphasis on the importance of reciprocal interactions between current and planned land use changes and the critical role of public transit accessibility. Results suggest that residential densification and upzoning processes reinforce each other. Urban residential upzoning can significantly promote the probability of parcel-level residential densification, even though it does not always lead to an immediate market response in every location. More importantly, the residential density increases are found to induce further plan/zoning modifications in nearby areas, indicating the presence of feedback loops in this dynamic relationship. There is also evidence of the positive influence of public transit accessibility. Single-family residential land parcels with greater access to high-quality transit services show a higher level of densification and upzoning probabilities when all other conditions are held constant. Such positive effects are detected not only in existing high-quality transit areas but also in locations where public transit services will be available in the future.

Phd Dissertation

Modeling and Planning for Future Multimodal Transportation with Household-owned Automated Vehicles

Abstract

Driverless (or fully-automated) vehicles (AVs) are expected to fundamentally change how individuals and households travel and how vehicles interact with roadway infrastructure. Privately-owned AVs (PAVs), when operated within households, offer travel options that distinguish them from conventional vehicles (CVs), such as remote parking, returning home to park, and serving other household members. These options—available through deadheading—can lead to an increase in vehicle miles traveled (VMT). The goals of this dissertation are to (i) explore the expected travel patterns of PAVs, (ii) analyze their impacts on transportation system performance, and (iii) propose design and policy changes to mitigate the negative impacts of PAVs and leverage their benefits.In this context, this dissertation presents three models and corresponding case studies. First, I propose a parking assignment model to analyze the impact of PAV parking behavior on travel patterns and parking facility demand and performance. The case study finds that significant VMT increases occur due to PAVs traveling to remote parking locations after dropping off travelers at activity locations, and that balancing fees and capacities of parking spaces can reduce the extra VMT. Second, I introduce a new policy and infrastructure system aimed at reducing VMT that is similar to a park-and-ride (PNR) system. Instead of traditional fixed-route transit, my proposed system includes transfer stations where travelers can switch from their PAVs to on-demand, door-to-door shared-use AVs (SAVs) that enhance traveler convenience and service reliability. By optimizing transfer station locations, the case study demonstrates significant reductions in both VMT and vehicle hours traveled (VHT) within the region. Third, I extend the routing and scheduling of PAVs to the decision-making process within households. I introduce the Household Activity Pattern Problem with AV-enabled Intermodal Trips (HAPP-AV-IT) that incorporates SAV, public transit, and transit-based intermodal travel options. The case study results reveal that travelers are likely to choose long deadheading options, such as returning home, to optimize household vehicle operations. The model also demonstrates that intermodal trips can reduce both the household’s travel distance and overall travel costs. Although the precise performance of AVs on road networks remains uncertain, the findings of this dissertation suggest that additional VMT from PAV deadheading could negatively affect transportation systems. As we move closer to the era of widespread AV adoption, it becomes increasingly important for planners and researchers to develop policies and infrastructure systems that reduce PAV deadheading miles. The methodological advancements and practical insights presented in this dissertation provide a strong foundation for addressing these challenges and preparing for the transformative impact of AVs.

policy brief

What Challenges Can Arise from Coordinating Housing Development with Transportation?

Abstract

More systematic coordination between transportation and housing development is increasingly recognized as a promising strategy for creating more sustainable communities. One approach is to encourage higher density affordable housing developments near transit or in similarly transportation-efficient areas, such as locations with low vehicle miles traveled (VMT). However, little is known about how transportation access should be considered in guiding housing development, what challenges can arise from coordinating housing development with transportation, and what the state can do to better deal with these challenges and achieve more equitable residential densification.

This brief examines equity issues and other challenges that may arise in pursuing transportation-informed housing development. Specifically, it touches on the potential impacts of Senate Bill 743, which made it easier to build more housing in low VMT locations by shifting the way traffic impacts from new housing development are evaluated under the California Environmental Quality Act. It also explores ways to achieve more inclusive development in non-rail transit areas which have received less attention compared to rail transit areas.