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Open Access Publications from the University of California

The primary mission of the Institute is research - cross-disciplinary inquiries into emerging transportation issues with great societal significance. It draws upon campus researchers and graduate students from a variety of disciplines, and also upon other universities and research centers around the world.

Residential solar water heating: California adopters and their experiences


Solar water heating provides domestic hot water with lower greenhouse gas emissions compared to more typical natural-gas water heating. Solar water heating has a long history, particularly in places where the climate is favorable, such as California where state-backed incentive programs have been successful in creating small bursts of adoption. However, widespread adoption of solar water heating has not occurred in California despite these conditions. This research surveyed 227 single-family households with solar water heating across the state of California to understand their motivations and experiences, and draw implications regarding barriers to adoption. The survey explored households’ experiences across five stages of adoption, as outlined in Rogers’ Diffusion of Innovation theory: Knowledge, Persuasion, Decision, Implementation, and Confirmation. Findings revealed challenges at each stage. Most notably, prevalent disappointment in lower-than-expected energy and bill savings (31%) and high rates of technical problems (41%) appear to be the most significant issues.

Cover page of Cohousing by Any Other Name: A Framing Study Exploring Ideological Barriers to Adoption of Collectivist Housing Options

Cohousing by Any Other Name: A Framing Study Exploring Ideological Barriers to Adoption of Collectivist Housing Options


Recent research suggests there is broader interest in cohousing in the US than its current niche market suggests. However, the lack of ideological diversity among cohousing adopters does not seem malleable. Cohousing adopters are predominately liberal and liberal ideology strongly predicts interest in cohousing. This research explored perceptions (including misperceptions) of cohousing and tested whether framing the concept differently could make it more appealing to Republicans and conservatives. Survey participants were randomly assigned to receive one of two versions of a survey, identical in all ways except in one version the term pocket neighborhoods was substituted for cohousing. Results revealed substantial misunderstanding of the concept of cohousing, particularly that it involves multiple unrelated households living under the same roof. There was no framing effect; those who identified as Republican or conservative did not find cohousing more appealing when it was called pocket neighborhoods. The most cited perceived benefits of cohousing were social interaction, relationships, and support, while lack of privacy and personal space topped the list of drawbacks. Understanding these common perceptions about cohousing can help stakeholders communicate more effectively about this model that promises many benefits to an apparently untapped prospective market.

Cover page of Nudging consumers toward greener air travel by adding carbon to the equation in online flight search

Nudging consumers toward greener air travel by adding carbon to the equation in online flight search


This study explores the potential to promote lower-emissions air travel by providing consumers with information about the carbon emissions of alternative flight choices in the context of online flight search and booking. We surveyed over 450 employees of the University of California, Davis, asking them to choose among hypothetical flight options for university-related business trips. Emissions estimates for flight alternatives were prominently displayed alongside cost, layovers and airport, and the lowest-emissions flight was labeled “Greenest Flight”. We found an impressive rate of willingness to pay for lower-emissions flights: around $200/ton of CO2E saved, a magnitude higher than that seen in carbon offsets programs. In a second step of analysis, we estimated the carbon and cost impacts if the university were to adopt a flight-search interface that prioritizes carbon emissions information and displays alternatives from multiple regional airports in their employee travel-booking portal. We estimated potential annual savings of 79 tons of CO2E, while reducing airfare costs by $56,000, mainly due to an increased willingness of travelers to take advantage of cheaper nonstop (lower-emissions) flights from a more distant airport in the region over indirect flights from their preferred airport for medium-distance flights. Institutionalizing this “nudge” within organizations with large travel budgets could have an industry-wide impact in aviation.

Low-Carbon Energy Generates Public Health Savings in California


California's goal to reduce greenhouse gas (GHG) emissions to a level that is 80 % below 1990 levels by the year 2050 will require adoption of low-carbon energy sources across all economic sectors. In addition to reducing GHG emissions, shifting to fuels with lower carbon intensity will change concentrations of short-lived conventional air pollutants, including airborne particles with a diameter of less than 2.5 µm (PM2.5) and ozone (O3). Here we evaluate how business-as-usual (BAU) air pollution and public health in California will be transformed in the year 2050 through the adoption of low-carbon technologies, expanded electrification, and modified activity patterns within a low-carbon energy scenario (GHG-Step). Both the BAU and GHG-Step statewide emission scenarios were constructed using the energy–economic optimization model, CA-TIMES, that calculates the multi-sector energy portfolio that meets projected energy supply and demand at the lowest cost, while also satisfying scenario-specific GHG emissions constraints. Corresponding criteria pollutant emissions for each scenario were then spatially allocated at 4 km resolution to support air quality analysis in different regions of the state. Meteorological inputs for the year 2054 were generated under a Representative Concentration Pathway (RCP) 8.5 future climate. Annual-average PM2.5 and O3 concentrations were predicted using the modified emissions and meteorology inputs with a regional chemical transport model. In the final phase of the analysis, mortality (total deaths) and mortality rate (deaths per 100 000) were calculated using established exposure-response relationships from air pollution epidemiology combined with simulated annual-average PM2.5 and O3 exposure. Net emissions reductions across all sectors are −36 % for PM0.1 mass, −3.6 % for PM2.5 mass, −10.6 % for PM2.5 elemental carbon, −13.3 % for PM2.5 organic carbon, −13.7 % for NO x , and −27.5 % for NH3. Predicted deaths associated with air pollution in 2050 dropped by 24–26 % in California (1537–2758 avoided deaths yr−1) in the climate-friendly 2050 GHG-Step scenario, which is equivalent to a 54–56 % reduction in the air pollution mortality rate (deaths per 100 000) relative to 2010 levels. These avoided deaths have an estimated value of USD 11.4–20.4 billion yr−1 based on the present-day value of a statistical life (VSL) equal to USD 7.6 million. The costs for reducing California GHG emissions 80 % below 1990 levels by the year 2050 depend strongly on numerous external factors such as the global price of oil. Best estimates suggest that meeting an intermediate target (40 % reduction in GHG emissions by the year 2030) using a non-optimized scenario would reduce personal income by USD 4.95 billion yr−1 (−0.15 %) and lower overall state gross domestic product by USD 16.1 billion yr−1 (−0.45 %). The public health benefits described here are comparable to these cost estimates, making a compelling argument for the adoption of low-carbon energy in California, with implications for other regions in the United States and across the world.

Cover page of How Do Small Businesses Experience Energy Reports?

How Do Small Businesses Experience Energy Reports?


How do small businesses experience energy reports that benchmark their performance relative to similar businesses and provide recommendations to save energy? There is a large body of research focused on energy feedback in the residential sector, but significantly less in the commercial sector. Studies in both sectors have focused on the effectiveness of feedback in terms of savings outcomes, while relatively little is known about how customers experience the interface itself. This paper presents a synthesis of results from a series of user research studies conducted with small- and medium-sized enterprises (SMEs) in Canada, the United States, and Australia. Results provide insights into aspects of energy reports business customers attend to or ignore, what information they value, whether and how they take action based on the reports, and barriers to taking action. Our findings highlight distinct areas utilities can focus on to improve business energy reports, including ways to reduce barriers to action and the need for energy reports to be carefully and precisely tailored.

Cover page of Using occupant feedback to drive energy efficiency across an entire university campus

Using occupant feedback to drive energy efficiency across an entire university campus


Despite the significant amount of energy spent on Heating, Ventilation, and Air Conditioning (HVAC) at universities, thermal comfort conditions in campus buildings are frequently poor. Conventional HVAC management systems at universities are typically out of the hands of building occupants and facilities management departments have limited resources to involve them. These factors can lead to over-heating or over-cooling and undiagnosed mechanical issues. Previous research has shown that thermal comfort feedback, or participatory thermal sensing, can simultaneously improve energy efficiency and occupant comfort in university buildings. However, these studies have been limited to single campus buildings and restricted populations of occupants. The success, scalability, and sustainability of any participatory thermal sensing program is dependent upon ongoing participation that is meaningful to occupants and useful to facilities management. Therefore, research is warranted to explore patterns of voluntary participation, thermal comfort, and occupant satisfaction in extended, campus-wide deployments of participatory thermal sensing programs. The present research begins to address these gaps in the context of an 18-month, campus-wide deployment of TherMOOstat, a participatory thermal sensing app and HVAC management system at University of California, Davis.

Cover page of Diffusion of Feedback: Perceptions and Adoption of Devices in the Residential Market

Diffusion of Feedback: Perceptions and Adoption of Devices in the Residential Market


Providing households with energy feedback is widely promoted as a conservation strategy and its effectiveness has been established in field studies. However, such studies actively recruit participants and little is known about naturalistic consumers. Despite hundreds of products emerging, few have taken hold in the market. Diffusion of innovation is a theory of technology adoption that details both the general process by which innovation spreads as well as the individual process of technology adoption. The current study analyses survey data from 836 individuals through a diffusion framework to assess the current and potential market of energy feedback. Questions related to knowledge and perceptions of feedback reveal important insights about customer acceptance and statistical comparison of adopters and non-adopters identify key characteristics related to adoption. Implications for the design and marketing of feedback technologies are discussed.

Cover page of OBDEnergy: Making Metrics Meaningful in Eco-driving Feedback

OBDEnergy: Making Metrics Meaningful in Eco-driving Feedback


This paper describes an eco-driving feedback system, OBDEnergy. Twenty-six drivers described their understanding of environmental impacts of driving before and after using OBDEnergy. Before OBDEnergy, participants discussed impacts in abstract, global terms (pollution, global warming). After OBDEnergy, participants appealed to concrete reference points (gallons of gas, trees required) with calculations and comparisons. We conclude that user-centered eco-driving feedback can contribute to pro-environmental behavior via increased awareness of the concrete environmental impacts of driving.

Cover page of Review of technical literature and trends related to automobile mass-reduction technology

Review of technical literature and trends related to automobile mass-reduction technology


Past automotive trends, ongoing technology breakthroughs, and recent announcements by automakers make it clear that reducing the mass of automobiles is a critical technology objective for vehicle performance, carbon dioxide (CO2) emissions, and fuel economy. Vehicle mass-reduction technology offers the potential to reduce the mass of vehicles without compromise in other vehicle attributes, like acceleration, size, cargo capacity, or structural integrity. As regulatory agencies continue to assess more stringent CO2 and fuel economy standards for the future, it is unclear the exact extent to which vehicle mass-reduction technology will be utilized alongside other efficiency technologies like advanced combustion and hybrid system technology. This report reviews ongoing automotive trends, research literature, and advanced concepts for vehicle mass optimization in an attempt to better characterize where automobiles – and their mass in particular – might be headed.