INTRODUCTION A plug-in hybrid electric vehicle (PHEV) is a type of hybrid electric vehicle that can use both grid electricity stored in batteries, and a liquid fuel as sources of energy. The use of grid electricity as an energy source reduces the use of conventional fuel and allows a PHEV to achieve reductions in greenhouse gas emissions, criteria emissions, and fueling costs [1]. Electrical energy is stored on-board a PHEV electrochemically in batteries, which are only able to store enough energy to drive the vehicle for a limited range. This means that a PHEV will generally operate in two modes: a charge depleting (CD) mode, in which the energy stored in the batteries will contribute to powering the vehicle, and a charge sustaining (CS) mode, in which conventional fuel provides all of the required driving energy and the net change in battery energy is zero. PHEVs that drive farther than their CD range use both CD and CS modes of driving. Because CD mode and CS mode are fundamentally different in terms of their energy sources, it is necessary to quantify and communicate the effect of each the two modes on metrics of vehicle fueling cost, emissions, and petroleum use. To this end, the SAE J2841 standard deines the concept of utility factor (UF), a method of weighting vehicle energy consumption in both CD and CS modes. SAE J2841 uses the National Household Transportation Survey (NHTS) as a model of consumer driving to provide a real-world basis for weighting Actual Versus Estimated Utility Factor of a Large Set of Privately Owned Chevrolet Volts John Smart Idaho National Lab. Thomas Bradley and Shawn Salisbury Colorado State Univ. ABSTRACT In order to determine the overall fuel economy of a plug-in hybrid electric vehicle (PHEV), the amount of operation in charge depleting (CD) versus charge sustaining modes must be determined. Mode of operation is predominantly dependent on customer usage of the vehicle and is therefore highly variable. The utility factor (UF) concept was developed to quantify the distance a group of vehicles has traveled or may travel in CD mode. SAE J2841 presents a UF calculation method based on data collected from travel surveys of conventional vehicles. UF estimates have been used in a variety of areas, including the calculation of window sticker fuel economy, policy decisions, and vehicle design determination. The EV Project, a plug-in electric vehicle charging infrastructure demonstration being conducted across the United States, provides the opportunity to determine the real-world UF of a large group of privately owned Chevrolet Volt extended range electric vehicles. Using data collected from Volts enrolled in The EV Project, this paper compares the real-world UF of two groups of Chevrolet Volts to estimated UF's based on J2841. The actual observed leet utility factors (FUF) for the MY2011/2012 and MY2013 Volt groups studied were observed to be 72% and 74%, respectively. Using the EPA CD ranges, the method prescribed by J2841 estimates a FUF of 65% and 68% for the MY2011/2012 and MY2013 Volt groups, respectively. Volt drivers achieved higher percentages of distance traveled in EV mode for two reasons. First, they had fewer long-distance travel days than drivers in the national travel survey referenced by J2841. Second, they charged more frequently than the J2841 assumption of once per day - drivers of Volts in this study averaged over 1.4 charging events per day. Although actual CD range varied widely as driving conditions varied, the average CD ranges for the two Volt groups studied matched the EPA CD range estimates, so CD range variation did not affect FUF results. CITATION: Smart, J., Bradley, T., and Salisbury, S., "Actual Versus Estimated Utility Factor of a Large Set of Privately Owned Chevrolet Volts," SAE Int. J. Alt. Power. 3(1):2014, doi:10.4271/2014-01-1803. 2014-01-1803 Published 04/01/2014 doi:10.4271/2014-01-1803 saealtpow.saejournals.org 30 Downloaded from SAE International by John Smart, Thursday, May 01, 2014 02:12:26 PM