I'm a daily rider of a motorcycle and felt I should note that while a motorcycle with a single rider uses less gas than a single person riding in a car, they create more pollution.
Well, this article is extremely biased.
First, it cites Athens as an example, where motorcycles reduced traffic, and still "let's ban them, there's better". Well, DOH, public transportation is better. Not to mention a proper way to fix the "motorcycle on a crossing" problem is by introducing additional space for motorcycles in front of cars, like in London. Or increase driver culture (which I hear in Greece is even worse than in USA).
Secondly, it doesn't take into account secondary effects, those of congestion on pollution. Whilst the motorcycle pollutes more per mile, I presume that is when they are driving at the same speed. It doesn't point out that motorcycle average speed in a city (due to white lining or going round stopped cars), it doesn't point out that a decelerating car uses far much energy than a motorcycle, etc.
The conclusions are equally biased, and whilst eliminating motorcycles is good IMHO, the fair way is by promoting public transport. The general impression I get is that the author basically says "let's tax the hell out of it" or just strait prohibit it.