Abstract: Plug-in Hybrid Electric Vehicles (PHEV) represent a promising pathway to reduce greenhouse gas emissions associated with the US transportation sector. A large-scale shift from gasoline-powered automobiles to PHEVs would inextricably link the US transportation system with its electric system. We build on  to perform a regional emissions analysis of a PHEV use pattern where PHEVs are charged at night and discharged during the day. We find that in some coal-intensive regions like the Midwest, charging PHEVs by burning coal may produce more emissions than burning gasoline. Overnight charging of PHEVs will deteriorate the system load factor by increasing off-peak demand. This may have deleterious effects on system infrastructure. We perform some simple simulations looking at the effect of off-peak PHEV charging on the performance of oilcooled substation transformers.