A study that analyzes the effectiveness of plug-in hybrid vehicles (PHEVs) to meet holistic environmental goals has been performed across the combined electricity and light-duty transportation sectors. PHEV penetration levels are varied from 0 to 60% and base renewable penetration levels are varied from 10 to 45%. Part 1 of the study focuses on CO2 emissions, fuel usage, and the renewable penetration level of individual and combined energy sectors. The effect on grid renewable penetration level depends on two factors: the additional vehicle load demand acting to decrease renewable penetration, and the controllability of vehicle charging acting to reduce curtailment of renewable power. PHEV integration can reduce CO2 emissions and fuel usage and increase the aggregate renewable energy share compared to the no-vehicle case. The benefits of isolated PHEV integration are slightly offset by increased CO2 emissions and fuel usage by the electric grid. Significant benefits are only realized when PHEVs are appropriately deployed in conjunction with renewable energy resources, highlighting important synergies between the electric and light-duty transportation sectors for meeting sustainability goals.