1 emission facts office of transportation and air quality epa420 f 05 003 february 2005 calculating emissions greenhouse gases key figures the us environmental protection agency epa developed this series four fact sheets to facilitate consistency assumptions practices in calculation from mobile sources they are intended as a reference for anyone estimating benefits pollution control programs average fuel economy federal highway administration fhwa use two different methodologies passenger vehicle although mobile6 s computer model vehicles estimates more current uses numbers developing gas inventory because consistent with methodology used estimate carbon diox ide miles per gallon mpg car 23 9 light duty truck 17 4 cars trucks combined 20 3 2 source run conducted 2003 based on test data annual trends reports fleet averages
