So far, so good – all of these mechanisms improve the efficiency with which a car travels. But, as a society, our interest lies in reducing total energy use, or total carbon emissions – and energy efficiency forms only one half of this picture. Our total carbon emissions also depend on the demand for travel. So, while improving the energy efficiency of cars by automating the driving process will reduce the carbon emissions of individual vehicles, the overall impact of this change will depend on how many people use them.