Recent itsdavis_dissertations items

The Hydrogen Fuel Pathway for Air Transportation

Fri, 13 Oct 2023 00:00:00 +0000

This thesis is a preliminary investigation into the technical feasibility and cost effectiveness of a hydrogen-fueled aviation system. A review on hydrogen aircraft reveals that designing and manufacturing hydrogen-powered aircraft is technically feasible. Major hydrogen supply technologies are available, but their capacity is far below the need of a hydrogen aviation system. A large airport such as San Francisco International Airport (SFO) can consume over 3000 metric tons of hydrogen per day, if its air traffic is entirely fueled by hydrogen. Such an energy flow could support over 3 million typical hydrogen fuel cell cars’ normal use. Airport liquid hydrogen cost modeling provides an estimation of hydrogen fuel cost as an aviation fuel. The cost is found to be 20%-90% higher than conventional jet fuel on a per energy basis, and supplying liquid hydrogen creates major electric power and land use challenge to the airport. The economies of scale are limited when hydrogen is supplied...

Behavioral Realism of Plug-In Electric Vehicle Usage: Implications for Emission Benefits, Energy Consumption, and Policies

Tue, 12 Apr 2022 00:00:00 +0000

Accelerating the adoption of plug-in electric vehicles (PEVs), is critical to reduce GHG emissions in the light duty vehicle sector. Conventional PEV usage and GHG assessments are largely based on assumptions drawn from stated preferences and choice experiments of potential or current PEV owners, or self-reported travel and refueling diaries of mainstream internal combustion engine(ICE) users. This dissertation focuses on observed behavior of current PEV users. I present three studies that seek to improve our understanding of PEV driving and charging typified by two levels of disaggregation- vehicle level and household level.

First study develops an analytical procedure to quantify what aspects of driving and charging behavior contributes to the gap between observed PHEV Utility Factors and Society of Automotive Engineers (SAE) J2841 expectations. Results indicated that depending on the PHEV range, roughly ±45% of deviations is attributable charging behavior. Daily mileage...

Dynamic Traffic Routing and Adaptive Signal Control in a Connected Vehicles Environment

Mon, 31 Jan 2022 00:00:00 +0000

This dissertation aims to study effective and efficient ways for both travelers and transportation authorities to consider the actions of the other side when they make their corresponding travel or management decisions, such that certain common goals, such as mitigating congestion, reducing cost in travel expenses and improving the overall reliability of the transportation system can be achieved.

A novel dynamic traffic routing (DTR) with an adaptive signal control framework is developed to utilize the fast developing wireless communication technologies that makes V2X (Vehicle To Everything) possible. The hyper-path based dynamic traffic routing method takes stochasticity of link travel time into consideration, which ensures robust and reliable routing decisions. In addition, online travel time updating is incorporated into the DTR model. The online updating presented in this dissertation uses both historical information (a priori knowledge) and new information, thanks...

Drivers of Change in a World of Mobility Disruption: An Overview of Long Distance Travel, Shared Mobility, and Automated Vehicles

Mon, 31 Jan 2022 00:00:00 +0000

Electrification, automation, and shared mobility, known as the 3 Revolutions (3R) will fundamentally change transportation globally. The 3 Revolutions are coming, and they will change existing travel behavior such as long-distance trips and create new questions such as who will drive for shared mobility and who will buy automated vehicles. Long distance travel, drivers for on-demand ride services, and the adoption of automated vehicles have been of recent interest to researchers, stakeholders, and policy makers but have just begun to be studied.

Long-distance travel research is limited due to the lack of robust data and the complexity of defining a long-distance trip. The patterns of infrequent long-distance trips are poorly understood especially compared to the better studied (and understood) local daily travel patterns. This study contributes to filling that gap by investigating the factors that affect the frequency of long-distance trips of Californian millennials...

Network Sensor Error Quantification and Flow Reconstruction Using Deep Learning

Mon, 31 Jan 2022 00:00:00 +0000

This study approaches the problem of quantifying the network sensor errors as a supervised learning problem and leveraging deep neural networks to map observed traffic flow counts to the systematic errors in the sensors. The author aims at building a model that could reconstruct the erroneous flow irrespective of the level of random noise in the sensors, which is unknown in the real-world. By reconstructing the erroneous flow with high accuracy, the transportation planners could gauge the true traffic flow demand in the network and can make informed infrastructure related decisions.

The study begins by simulating the traffic network under dynamic flow assignment settings to generate the base flow that is treated as the ground truth. The authors then introduce measurement errors to the base flow to generate the observed flow which is transformed into a multi-dimensional time-series tensor data, where each time step has dimension equal to the number of sensors in the network....

Investigation into Aging Mechanisms and Performance of Rubber-Modified Asphalt Binder and Mix

Thu, 2 Sep 2021 00:00:00 +0000

Crumb rubber modifier (CRM) produced from waste tires has been used in pavement engineering for more than half a century. This recycling methodology improves sustainable development because of environmental benefits of recycling scrap tires and because of improved performance of pavement materials when the recycled tire rubber is used as modifier in asphalt binders. This application improves both rutting and cracking resistance of asphalt pavement when an appropriate design is followed.

Adding the CRM to asphalt binders leads to modification of binder properties, including rheological properties and aging resistance. This modification alters pavement performance in-service. Previous studies found that rubber-modified binders had better aging resistance than their base binders. However, the mechanism of rubber modification on aging resistance was not well understood. This study aimed to explore this mechanism for rubber-modified binders. This study also evaluated the performance-related...

Policy Improvements of Private Transportation in US and China

Mon, 30 Aug 2021 00:00:00 +0000

This dissertation consists of three chapters that investigate policies aiming for improving private automobile transportation from different angles.

The first chapter focuses on the efficiency of marked versus unmarked on-street parking. The study uses computer simulation that assigns queues of randomly generated vehicles to marked and unmarked spaces using a parallel world method, to directly test which method is more efficient and accommodate more cars. The simulation results show that unmarked spacing is more efficient only when the curb is shorter, or not close to any integer times of the optimal length of one marked space, and when drivers are all considerate when choosing the parking location. This simulation study also finds vehicle downsizing only helps the owners of the downsized vehicles themselves, while making it more difficult for all other people to find parking.

The second chapter focuses on the engine size tax in China. Using regressions based on...

Conservation Strategies That Address Habitat Loss and Fragmentation: Implications for Forest Cover Change and Wildlife Behavior

Wed, 25 Aug 2021 00:00:00 +0000

Habitat loss and fragmentation is currently the primary driver of biodiversity decline. Community forest management and wildlife crossing structures are two common conservation strategies applied to mitigate habitat loss and fragmentation. Community forest management is an approach that enables local communities to participate in forest management in order to reduce deforestation, and crossing structures are intended to mitigate the negative impacts of roads in fragmenting the landscape. To implement efficient design, their effectiveness needs to be examined using rigorous and appropriate methods. Herein, I assess the efficacy of each in the context of counterfactual assessments and baseline conditions. Using Pemba Island, Tanzania, as a case study, I monitor Community forest management, and use unprotected areas as the baseline. For wildlife crossing structures I examine structures along California highways, and use adjacent wildland areas absent of roads as the baseline. I employ...

Integrated and Data-Driven Transportation Infrastructure Management through Consideration of Life Cycle Costs and Environmental Impacts

Tue, 12 Jan 2021 00:00:00 +0000

The main goal of this dissertation was to develop frameworks, quantitative models, and databases needed to support data-driven, informed, and integrated decision-making in managing the vast transportation infrastructure in California. Such a management system was envisioned to consider both costs and environmental impacts of management decisions, based on full life cycles of the infrastructure, and using reliable, high quality data that well represent local conditions in terms of materials and energy sources, production technologies, design methods, construction practices, and other critical parameters.

This PhD research consisted of three parts: 1) development of a comprehensive life cycle inventory (LCI) database for implementation of life cycle assessment (LCA) methodology in transportation infrastructure management in California. 2) Evaluation of current and potential sustainability actions at the state and local government levels through the development of frameworks,...

Critical Infrastructure Systems: Distributed Decision Processes over Network and Uncertainties