conference paper
conference paper
This paper investigates the effect of airline emissions charges on airline service quality, airfares, aircraft design features, and network structure, using a realistic and detailed theoretical model of competing duopoly airlines. These impacts are derived by analyzing the effects of an increase in the effective price of fuel, which is the path by which emissions charges will alter airline choices. The results show that emission charges will raise fares, reduce flight frequency, increase load factors, and raise aircraft fuel efficiency, while having no effect on aircraft size. Given that these adjustments occur in response to the treatment of an emissions externality that is currently unaddressed, they represent efficient changes that move society closer to a social optimum.
conference paper
Transit agencies are interested in integrating microtransit service with fixed-route transit (FRT) service to leverage the benefits of each mode. In an integrated FRT and microtransit system, fare structures for both FRT and microtransit services play an important role in influencing travelers’ behavior. This paper studies 10 different fare structures and their impacts on travelers’ behavior in the presence of an integrated FRT and microtransit system. We use a flexible agent-based FRT and microtransit modeling framework recently proposed by the authors to study fare structures. We analyze the impacts of fare structures on synthetic travelers in downtown San Diego and Lemon Grove, a small city in San Diego County. The results show that the intermodal transfer discount policy — where a traveler can use FRT freely when transferring from microtransit to FRT or receives a 50% discount on microtransit when transferring from FRT to microtransit — is the most promising. Under this fare structure, the subsidy per transit rider ($8.20 in downtown San Diego and $13.5 in Lemon Grove), transit user out-of-pocket costs ($1.27 in downtown San Diego and $1.71 in Lemon Grove), and auto mode share (80.6% in downtown San Diego and 86.5% in Lemon Grove) are the lowest of any fare structure.
conference paper
published journal article
published journal article
BACKGROUND AND AIM: There is minimal evidence of relationships between maternal air pollution exposure and spontaneous premature rupture of membranes (SPROM), a critical obstetrical problem that can significantly increase maternal and fetal mortality and morbidity. No prior study has explored the PROM risk related to specific components of particulate matter with aerodynamic diameters of ≤ 2.5 µm (PM₂.₅). We examined associations between maternal exposure to nitrogen dioxide (NO₂), ozone (O₃), PM₂.₅, PM10, and PM₂.₅ constituents and SPROM. METHOD: A large retrospective cohort study was conducted and included 427,870 singleton live births from Kaiser Permanente Southern California during 2008-2018. Monthly averages of NO₂, O₃ (8-h daily maximum), PM₂.₅, and PM10 were measured using empirical Bayesian kriging based on measurements from monitoring stations. Data on PM₂.₅ sulfate, nitrate, ammonium, organic matter, and black carbon were obtained from a fine-resolution model. A discrete time approach with pooled logistic regressions was used to estimate associations throughout the pregnancy and based on trimesters and gestational months. The quantile-based g-computation models were fitted to examine the effects of 1) the air pollution mixture of four pollutants of interest and 2) the mixture of PM₂.₅ components. RESULTS: There were 37,857 SPROM cases (8.8%) in our study population. We observed relationships between maternal exposure to all four pollutants and SPROM. PM₂.₅ sulfate, nitrate, ammonium, and organic matter were associated with higher SPROM risks in the single-pollutant model. Mixture analyses demonstrated that the overall effects of the air pollution mixture and PM₂.₅ mixture in this study were mainly driven by O₃ and PM₂.₅ nitrate, respectively. Underweight mothers had a significantly higher risk of SPROM associated with NO₂. CONCLUSIONS: Our findings add to the literature on associations between air pollution exposure and SPROM. This is the first study reporting the impact of PM₂.₅ constituents on SPROM.
book/book chapter
published journal article
Most discrete choice models assume steady state conditions and a fully equilibrated system when estimating unknown coefficients from real-world data. However, the estimated model can be biased when the data set used for the model estimation was drawn from non- or less-equilibrated traveler behavior. The resulting biased model could lead to a misunderstanding of the system. Such effects on discrete choice model estimation were examined by performing Monte Carlo simulation experiments. A day-to-day dynamic evolutionary framework was used to observe changes in traveler’s choice and to compare the estimated results during the adjustment process with the true behavior parameters.
published journal article
The equations governing the dynamic deformation of an elastic solid are considered as a symmetric hyperbolic system of linear first-order partial-differential equations. The characteristic properties of the system are determined and a numerical method for obtaining the solution of mixed initial and boundary-value problems in elastodynamics is presented. The method, based on approximate integral relations along bicharacteristics, is an extension of the method proposed by Clifton for plane problems in dynamic elasticity and provides a system of difference equations, with second-order accuracy, for the explicit determination of the solution. Application of the method to a problem which has a known solution provides numerical evidence of the convergence and stability of the method.
book/book chapter