 The analysis found that marginal emission rates are more than three times as large in the Upper Midwest compared to the Western U.S., and within regions, rates for some hours of the day are more than twice those for others.Applying the results of the marginal analysis to plug-in electric vehicles, the NBER researchers found that the emissions of charging PEVs vary by region and hours of the day.In some regions, such as the Western U.S. and Texas, emissions per mile from driving PEVs are less than those from driving a hybrid car.