Fully-electric vehicles have the lowest carbon emission rates and are thus the most eco-friendly in terms of net emissions, according to the U.S. Department of Energy. However, some environmental scientists argue that the source of electricity for your electric vehicle, such as renewable energy sources, determines how sustainable it truly is. Fully-gasoline vehicles are the least eco-friendly option in terms of net emissions, but that doesn't mean you can't make sustainable choices as a traditional car owner. Maintaining your combustion engine vehicle well and driving efficiently is a way for non-EV owners to cut down on their emissions.