Same goes for acetone as a fuel additive. I experimented with that for a year and found no real difference in fuel mileage. What did work remarkably well on my Jeep, and what will probably work extremely well on a bus at highway speeds, is an air dam that goes almost down to the road. The air dam that I put on my Jeep increased my mileage by 16% to 20%, depending on speed. I tested that over several years, and the results were constant. If I drove at 50 mph in a steady state condition, with the air dam on the front of the car I could routinely get 28 mpg in a 4 cylinder Jeep. At 75 mph I got about 23 mpg. If you have an air dam and get behind the right truck (drafting), you can get even better mileage.
I'd put an air dam on my
bus, but it won't go fast enough to make a difference. They are only effective starting at the 45-50 mph range, and my bus only goes 50 on a downhill straightaway.
This discussion is essentially what got me kicked out of Arky's Yahoo group.