Abstract:Plug-in hybrid electric vehicles (PHEVs), which run on both electricity from the grid and gasoline, are touted as providing some of the societal and environmental benefits of electric vehicles for a large portion of motorists’ daily travel, while also acting as a transitional technology toward fully electric vehicles. To test analysts’ assumptions about how PHEV users will recharge their vehicles, the observed recharging behaviors of forty households that participated in a PHEV demonstration in Northern California are reported. Recharging behavior is summarized across all households’ last week of their four-week PHEV trial period with regards to the time-of-day, frequency of plugging-in, and electricity demand to recharge the vehicles. While the means of the frequency distribution of plug-in events among demonstration households is similar to prior recharging assumptions made by analysts, the distributions are not symmetrical about the mean and there exists a large variation in both the average number of times households plugged-in per day and the average energy per plug-in event. Further, there is no strong correspondence between the number of daily plug-in events and total daily electricity demand. The range of behaviors reported here support the contention that the success of PHEVs in meeting energy and emissions goals relies on PHEV users’ recharging and driving behavior as much or more as on PHEV designs.