This is somewhat related and interesting repost:
Emissions Test: Car vs. Truck vs. Leaf Blower
Cliffs: 0.03L leaf blower is way dirtier than 6.2L 411hp truck.
On the subject of bike ownership cost... I sold my last bike like 2 years ago, but even at 50mpg, it was arguably more expensive and more hassle to operate than a 30mpg car. It could eat a rear tire in no time flat, eat brake pads, and is very maintenance intensive.
Chain clean + lube every 400 miles.
Solid lifters that need to be adjusted.
$50-100 gloves wearing out after only 10k miles.
Helmet visor replacements.
More expensive and more frequent oil changes.
Fork rebuilds every 2 years or so.
Etc.
Mine was definitely not greener than a car as it had zero emissions controls.