Plug-in electric vehicle (PHEV) technology is seen as promising technology for reducing oil use, improving local air quality, and/or possibly reducing GHG emissions to support a sustainable transportation system. This paper examines the usage of household vehicles to support assessment of the market potential of plug-in hybrid electric vehicles (PHEVs), the higher purchase price of which requires high usage rates to pay off the investment in the technology. According to the 2009 National Household Travel Survey (NHTS), about 40% of household vehicles were not used on the survey travel day . This study analyzed household vehicle use and non-use by vehicle type, age, area type (metropolitan statistical area [MSA] and non-MSA), and population density. Vehicles used on survey day with or without a reported travel time and distance in the survey are considered “vehicles used”. All others are referred to as “vehicles not used”. We divided the “vehicles not used” into three categories: 1) left at home while other household vehicles were used; 2) not used because travelers used other modes; and 3) no household trips. The “vehicle used” consists of two categories: 1) those with distance and time data and 2) those with no travel data. Within these five categories, vehicles were subdivided according to four vehicle types: car, van, SUV, and pickup. Each vehicle type was further subdivided in two age groups: 10 years or less (≤10) and more than 10 years (>10). In addition, vehicle usage was compared in both MSAs and non-MSAs and during weekdays and weekends. Results indicate that most vehicles—especially pickups—are not used because the households own and use other vehicles. Moreover, SUVs—especially newer SUVs (≤10 years)—are the most utilized vehicle type and should be strongly considered as a primary vehicle type for PHEVs, in addition to cars.
 Federal Highway Administration, “2009 National Household Travel Survey,” US Department of Transportation, Washington DC. http://nhts.ornl.gov/download.shtml
 A. Elgowainy, J. Han, L. Poch, M. Wang, A. Vyas, M. Mahalik and A. Rousseau, “Well-to-Wheels Analysis of Energy Use and Greenhouse Gas Emissions of Plug-In Hybrid Electric Vehicles,” Center for Transportation Research, Argonne National Laboratory Report ANL/ESD/ 10-1. http://www.transportation.anl.gov/pdfs/TA/629.PDF
 A. D. Vyas, D. J. Santini, M. Duoba and M. Alexander, “Plug-In Hybrid Electric Vehicles: How Does One Determine Their Potential for Reducing US Oil Dependence?” Proceedings of the 23rd Electric Drive Vehicle Symposium (EVS 23), Anaheim, 2007.
 A. D. Vyas, D. J. Santini and L. R. Johnson, “Potential of Plug-In Hybrid Electric Vehicles to Reduce Petroleum Use: Issues Involved in Developing Reliable Estimates,” Transportation Research Record, 2009, pp. 55-63. doi:10.3141/2139-07
 A. Elgowainy, Y. Zhou, A. D. Vyas, M. Mahalik, D. Santini and M. Wang, “Impacts of Plug-In Hybrid Electric Vehicles Charging Choices in 2030,” Proceedings of the 91st Annual Meeting of the Transportation Research Board, Washington DC, 2012.
 A. Taylor III, “The Birth of the Prius,” Fortune, 2006. http://money.cnn.com/magazines/fortune/fortune_archive/2006/03/06/8370702/
 T. Stephens, J. Sullivan and G. A. Keoleian “A Microsi-mulation of Energy Demand and Greenhouse Gas Emissions from Plug-In Hybrid Electric Vehicle Use,” Proceedings of the Electric Vehicle Symposium, Los Angeles, 6-9 May 2010.
 Da Costa, F. Badin and A. Rousseau, “Fuel Consumption Potential of Different Plug-In Hybrid Vehicle Architectures in the European and American Contexts,” Proceedings of the Electric Vehicle Symposium, Los Angeles, 6-9 May 2010.