Apr 28, 2021 · Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown. 8.89 × 10-3 metric tons CO 2 car/truck average × 1/22.5 miles per gallon car/truck average × 1 CO 2, CH 4, and N 2 O/0.993 CO 2 = 4.60 metric tons CO 2 E/vehicle /year. Sources EPA (2020).