Suggested Citation: Kurani, Kenneth S., Tai Stillwater, Matt Jones, Nicolette Caperello (2013) Ecodrive I-80: A Large Sample Fuel Economy Feedback Field Test . Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-13-15
Energy feedback in the vehicle dashboard is one method to engage drivers in energy saving driving styles. In contrast to the occasional broadcasting of general driving tips, in-vehicle energy feedback gives drivers access to accurate real-time information about their specific driving situation on an ongoing basis. The increasing prevalence of such feedback in new vehicles suggests a belief that such feedback is effective. However, there is little reliable evidence of the effectiveness of energy feedback in real-word driving in passenger vehicles. This study begins to fill this gap. This report presents the results of a large sample eco-driving feedback study that includes 118 drivers (140 driver-vehicle combinations); the drivers resided in selected cities along the Interstate-80 corridor from San Francisco, CA to Reno and Sparks, NV. Participants were given a commercially available fuel consumption recording and display device to use in their personal vehicle for two months. The first month the display was left blank to record a baseline of driving and fuel consumption: the second month the display was switched on. The devices displayed one of three screen designs spanning a variety of feedback modes; household drivers were randomly assigned a screen. Using a mixed-effects linear model that controls for road grade and weather conditions, we find a statistically significant decrease of 2.7% in fuel consumption rate (grams of gasoline per meter) between the without and with-feedback months over all driver-vehicles and screens. Drivers reduced their median trip speeds and mean acceleration rates during the with-feedback phase. The effect of the three display designs ranged from a mean 1.6% to 2.9% reduction. Differences in the reduction in fuel consumption by driver sex were larger: 1.9% for men vs. 5.0% for women. Far larger savings appear possible if driver motivations can be linked to feedback design: alignment of pre-feedback driver goals with screen designs resulted in one group achieving a 22% improvement. Overall, we estimate that if each driver had received the optimal screen for his or her goal the total mean reduction would have been 9.2%—a threefold increase over the random assignment. Analysis of households’ exit interviews revealed that while many households claim achieving good fuel economy was a goal of their driving, few could name more than three things they could do or actually do to increase fuel economy. Motivations for higher fuel economy span a range of cost savings, energy security, conservation, environmental protection, and climate change. A thematic analysis of the interview text produces a structure of four main themes, i.e., driving contexts, sense of personal control over energy use, learning, and durability over time of behaviors. Feedback can affect each of these themes and bridge between them, e.g., increasing a sense of personal control over fuel economy can be accomplished by learning via feedback how personal actions affect fuel economy across driving contexts.