It oculd easily be the case that the Hummer might still have a lower RATIO than a modern motorcycle but I have a hard time buying the idea that a late model bike would produce more actual pollution. Particularly if the bike had fuel injection and particularly if it was something like a FI version of something like a 250 - 400 cc on/off road b ike which got 60 mpg or better. The Kawasaki 250KLR's fuel mileage was phenomenal.
I ride a Yamaha VStar 1300. Fuel injected and equipped with a cat converter. 45+ mpg riding 2 up. I suspect my bike will meet all the Fed regs even for cars. >p<regards - red
Over there they would refer to US cars as “Dreck Schleuder” (Filth slinger) and ironically this was years after in the US cars has catalytic converters, were running on unleaded fuel, and had pollution pumps. All the way into to 90s they were driving leaded and without catalytic converts for the most part, but that didn't stop them from snubbing their noses at American cars and calling them “filthy, uneconomical, polluting.... you name it.”