conference paper
conference paper
Over the years the capacity drop phenomenon at freeway bottlenecks has remained a topic of interest and intrigue. Capacity drop has an undeniable impact on freeway performances, directly affecting the throughput. Various studies have tried to measure, predict, and model capacity drop. In this paper, the authors integrate a simplistic lane changing model and an acceleration model together into the Cell Transmission Model framework. The capacity drop is modeled as a combined effect of a lane changing area upstream of the bottleneck location and an acceleration region downstream. Each lane changing vehicle is considered to contribute towards density on two lanes during the lane changing maneuver as it effects the following vehicles on both the original and target lanes. This effect is modeled through the introduction of a â??perceived densityâ?? variable. This perceived density is obtained by scaling the actual density up by the lane-changing intensity, and is used to determine the demand at the bottleneck. A demand function linearly decreasing in density under over-saturated conditions is used to model the acceleration process of vehicles as they discharge from the bottleneck. It is shown that the capacity drop can then be predicted from calibrated demand-supply functions and lane changing intensity.
published journal article
conference paper
This paper analyzes responses to a 2010 national survey of 835 US households to explore consumer preferences among five types of vehicles that differ in propulsion technology (gasoline, hybrid electric (HEV), compressed natural gas (CNG), hydrogen fuel cell (HFC), and electric (EV)), vehicle cost, fuel cost, fuel availability, vehicle range, and CO2 emissions during operation. Although gasoline-fueled vehicles are still preferred, there was strong interest in alternatives to gasoline vehicles, and especially in HEVs, while EVs are least popular. The authors estimated a panel rank-ordered mixed logit model to understand the impact of vehicle characteristics and of the socio-economic characteristics of respondents on their preferences for alternative fuel technologies. With the exception of CNG, respondents prefer alternative propulsion technology in cars as opposed to pick-up trucks, sport utility vehicles (SUV), or minivans. The region where people live is not statistically significant. Education matters only in the case of HEVs, but gender has no significant impact, and the influence of age is technology specific. It was found that environmental attitudes are strong predictors of AFV support, particularly for HFC vehicles and EVs. In addition, the authors elicited trade-offs people are willing to make between vehicle cost, fuel cost, vehicle range, and refueling time. In spite of consumer interest for alternative-fuel vehicles, environmental benefits still take second place to economic considerations.
published journal article
Background Maternal exposure to traffic-related air pollution during pregnancy has been shown to increase the risk of adverse birth outcomes and childhood disorders. High-resolution metabolomics (HRM) has previously been employed to identify metabolic responses to traffic-related air pollution in adults, including pregnant women. Thus far, no studies have examined metabolic effects of air pollution exposure in utero on neonates. Methods We retrieved stored neonatal blood spots for 241 children born in California between 1998 and 2007. These children were randomly selected from all California birth rolls to serve as birth-year matched controls for children with retinoblastoma identified from the California cancer registry for a case control study of childhood cancer. We estimated prenatal traffic-related air pollution exposure (particulate matter less than 2.5 μm (PM2.5)) during the third-trimester using the California Line Source Dispersion Model, version 4 (CALINE4) based on residential addresses recorded at birth. We employed untargeted HRM to obtain metabolic profiles, and metabolites associated with air pollution exposure were identified using partial least squares (PLS) regression and linear regressions. Biological effects were characterized using pathway enrichment analyses adjusting for potential confounders including maternal age, race/ethnicity, and education. Results In total we extracted 4038 and 4957 metabolite features from neonatal blood spots in hydrophilic interaction (HILIC) chromatography (positive ion mode) and C18 reverse phase columns (negative ion mode), respectively. After controlling for confounding factors, partial least square regression (Variable Importance in Projection (VIP) ≥ 2) selected 402 HILIC positive and 182 C18 negative features as statistically significantly associated with increasing third trimester PM2.5 exposure. Using pathway enrichment analysis, we identified metabolites in oxidative stress and inflammation pathways as being altered, primarily involving lipid metabolism. Conclusion The metabolite features and pathways associated with air pollution exposure in neonates suggest that maternal exposure during late pregnancy contributes to oxidative stress and inflammation in newborn children.
working paper
This paper empirically investigates the impact of airport and airline supply characteristics on the air travel choices of passengers departing from one of three San Francisco Bay area airports and arriving at one of four airports in greater Los Angeles. It does so by estimating a conditional logit model for the market of air travel between both metropolitan areas in 1995, and using the estimated model to simulate three counterfactual scenarios. First, reducing access times to San Francisco International airport by 10% for all travelers increases the market share of that airport by 4.5%-point. United Airlines benefits from the reduced access times, as its market share increases by 2.9%-point. Second, reducing average delays at San Francisco International airport by 10% has similar aggregate effects to the first scenario, but indicates that leisure travelers value access time reductions more than reduced delays. Third, entry of Southwest airlines in San Francisco International airport increases the market share of Southwest airlines by 5%-point to 15-%point, depending on assumptions concerning its continuation of services at Oakland International Airport, and assuming that rival carriers do not respond in terms of prices or service levels.
published journal article
published journal article
Background: Benzene is classified as a Group 1 carcinogen in humans. A major pathway of benzene exposure is through inhalation of ambient air contaminated by emissions from motor vehicle exhaust, gas stations, industry, tobacco smoke, and other consumer products. Prior studies of benzene and lung cancer have been limited largely to occupational studies. We examined the association between outdoor air exposure to benzene and lung cancer risk in the large population-based Multiethnic Cohort Study (MEC), including four major U.S. racial/ethnic groups—African Americans, Latinos, Japanese Americans, and Whites. Methods: Ambient benzene exposure was estimated from EPA data from air monitoring stations that were within 20 km of residences of 97,288 MEC participants, largely from Los Angeles County, from the time-period of recruitment (1993-1996) through 12/31/2013. Cox proportional hazards models were used to examine the associations between time-varying benzene exposure and lung cancer risk (cases=2796), adjusting for age, sex, race/ethnicity, smoking, family history of lung cancer, marital status, education, occupation, use of nonsteroidal anti-inflammatory drugs, body mass index, alcohol consumption, physical activity, intake of total calorie, red and processed meats, and neighborhood (block group) socioeconomic status. Stratified analyses were conducted by sex, race/ethnicity, and smoking status. In addition, subgroup analysis was conducted by histologic cell-type (adenocarcinoma, squamous cell carcinoma, small cell carcinoma, large cell, and not otherwise specified carcinoma). Results: Ambient benzene exposure was associated with increased risk of lung cancer (per 1 ppb hazard ratio (HR)=1.18; 95% CI: 1.03-1.35). Slightly higher hazard ratios were observed in females (HR=1.28; 95% CI: 1.05-1.56) in comparison to males (HR=1.12; 95% CI: 0.92-1.35). There was evidence of heterogeneity in associations by race/ethnicity (p heterogeneity=0.02). Specifically, benzene exposure was associated with increased lung cancer risk among African Americans, Japanese Americans, and Latinos (HR ranged 1.18 to 1.42 per 1 ppb), but was inversely associated with risk among Whites. Also, similar associations were seen among ever smokers (HR=1.19; 95% CI: 1.03-1.37) and never smokers (HR=1.25; 95% CI: 0.82-1.89). Across histologic-cell types, a borderline statistically significant association was seen with adenocarcinoma, the most common cell type (HR=1.25, 95% CI: 0.99-1.58). A smaller hazard ratio was observed for squamous cell carcinoma, the stronger smoking-related cell type (HR=1.09, 95% CI: 0.81-1.47). Conclusions: Benzene exposure adversely impacts the risk of lung cancer in the general population but particularly in non-Whites after adjusting for smoking, occupational and other exposures. Additional large population-based studies are needed to confirm this finding and reinforce the need for stringent clear air laws.Citation Format: Iona Cheng, Chiuchen Tseng, Jun Wu, Juan Yang, Salma Shariff-Marco, Jennifer Jain, S. Lani Park, Scott Fruin, Timothy Larson, Scarlett Lin Gomez, Lynne Wilkens, Daniel Stram, Loic Le Marchand, Beate Ritz, Anna H Wu. Association between benzene, a hazardous air pollutant, and lung cancer risk: The Multiethnic Cohort Study [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr C052.
Phd Dissertation
Until recently, federal regulation required natural gas pipelines to bundle the sale of natural gas with its transportation. Gas fields connected to city markets through merchant carrier pipelines who bought and sold gas through long-term contracts. Gas buyers were unable to transact directly with gas producers; they were able to deal only through merchant pipelines. This structure nearly precluded gas markets; there were only a few spot markets and there was no futures market. Relaxed pipeline regulation has changed this; natural gas pipelines were permitted to unbundle gas from transportation and to offer pure transportation service. As more pipelines declared themselves to be “open access” pipelines, spot markets emerged and a futures market opened. Soon pipelines transported far more gas on behalf of their customers than they sold to them. By using and trading transportation on several pipelines, brokers and customers developed the ability to buy and sell gas at many points in the dense transmission grid. When enough pipelines opened themselves to transportation, the connected topology of the network could and did support geographic and intertemporal arbitrage. Monthly and daily spot gas field and citygate prices are examined to determine the extent to which these markets have become integrated. The empirical results show that prices converged and became more cointegrated across the network. The results of a vector autoregression model support the conclusion that by 1990, trading and arbitrage under the new market institutions enforced an equilibrium free of arbitrage opportunities at the field level. At the city market level, the no-arbitrage condition does not yet hold as strongly due to the restrictions placed on transferable transportation rights by state and local authorities. There are still limitations preventing full development of markets and competition in the pipeline network. In light of the dramatic increase in the efficiency of the natural gas market, there is no evidence to support the need for the Federal Energy Regulatory Commission or regulation. Regulation caused the price disparities and allocative inefficiency that markets eliminated.
Preprint Journal Article
Connected vehicle (CV) technology enables data exchange between vehicles and transportation infrastructure and therefore has great potentials to improve current traffic signal control systems. However, this connectivity might also bring cyber security concerns. As the first step in investigating the cyber security of CV-based traffic signal control (CV-TSC) systems, potential cyber threats need to be identified and corresponding impact needs to be evaluated. In this paper, we aim to evaluate the impact of cyber attacks on CV-TSC systems by considering a realistic attack scenario in which the control logic of a CV-TSC system is unavailable to attackers. Our threat model presumes that an attacker may learn the control logic using a surrogate model. Based on the surrogate model, the attacker may launch falsified data attacks to influence signal control decisions. In the case study, we realistically evaluate the impact of falsified data attacks on an existing CV-TSC system (i.e., I-SIG).