So, I'm trying to calculate amount of Tg CO2 Eq from heavy duty vehicles and I ran into problems. First, I looked at the US Greenhouse Inventory Report and it said that heavy duty vehicles accounted for 343 Tg CO2 Eq in 2003. Then I look at the well-to-wheel GHG Emissions in g/mile from Argonne National Lab for conventional diesel engine and it is 472 g/mile. And in 2003, the total VMT for heavy duty vehicles was 141000 million miles. So 472 * 141000 million = 66 Tg CO2 Eq. It is 5 times less than the value from the GHG inventory report. What am I missing here?