So, let's have a tutorial about emissions.....
1. GOVT isn't your friend
2. Corporations are after the bottom dollar, not your bottom dollar
3. #1&2 are in bed together. Corps being the little spoon
4. CAFE - corporate average fuel economy
Emissions are not your friend first off, driven by #1. There are different tiers and bins in said tiers. Based on HP ratings, displacement, GVW, and others determines what "bin" in the tier it has to achieve. At times there are "interim" calibrations that are allowed until finalized rules/regs are established.
After that is determined, a calibration is made to achieve said rating. CAFE is based on total vehicle sales and has to meet the standard. No auto maker knows what their number will be at the beginning of a year. They can project a number and base CAFE off historical data. NO automaker wants to give up CAFE credits for any reason if they don't have to. It's like their warm, fuzzy blanket for a rainy day.......so they keep them close.
This means that if they all of a sudden start selling the shit out of big vehicles and less little ones, their CAFE numbers will be off for that year. So, in order to satisfy their bed partner (govt/big oil), they would have to give up some of their precious CREDITS.......or they can do the govt/corporate thing and pass it along to the end user. Hence "revised" calibrations that allow them to satisfy their bin requirements for their CAFE requirements after the fact.
Lastly, emissions are driven by uneducated, corrupt govt peoples who have pockets lines by oil companies. In the guise of cleaner air, they will sell you something that uses more fuel to do the same amount of work. And for you diesel owners, they also get to sell you DEF which is a byproduct they didn’t have a huge market for before tier 4.
Follow the money, use common sense and you'll see the real story. If you think 26 - 30 mpg is good, you wouldn't believe what you could get with a motor calibrated for EFFICIENCY, not what the EPA says is clean.........2 VERY different things.
I hope this is less sensationalism. I can get out the crayons if needed.......