How replacing petroleum fuels with alternative liquids would change greenhouse gas emissions

One thing that is not obvious from the graph is that the 47% reduction in greenhouse gases attributed to replacing highway fuels with electricity from the grid assumes an average mix of electricity generation sources.  More than 83% of CO2 emissions from US electricity generation come from the half that comes from coal.  Although grid power to on-board batteries to on-board electric motors wastes only about half as much energy as an on-board internal combustion engine, the potential greenhouse gas improvement would be lost to the extent that shifting to electric vehicles results in the construction, or delays the retirement, of coal-fired power plants.  The marginal coal plant would emit about as much CO2 per vehicle mile as the petroleum fueled vehicles displaced.