Thanks for the link.
Very complicated calculation indeed. Including AC use in the new EPA calculation should bring the estimate closer to reality. When I hit 36.6 on my recent 300 mile trip, it was during a cool day and I had the AC off. I took shorter (~30 mile) highway trips before, but with the AC on, I averaged closer to 34 MPG. So a better calculation would include mixes of terrain variables (rural, suburban, urban, hilly/level, etc) and month-to-month temperature variations that would affect AC use and fuel combustion efficiency.
They also indicate the new calculation includes faster acceleration and higher cruising speed variables from the numbers established 40 years ago. What took them so long.