You mean how many people have yet to try riding a motorcycle?

You know what can not only do that, but more safely in rain-proof climate control and hauling your family and groceries too and rolling out one century after another?

A car.

Once you start making intermediate vehicles that fall somewhere between a bicycle and a car with some of the properties of each, you have to carefully consider what is lost vs. what is gained, how that impacts you individually and where it fits into society as a whole.

Let's be realistic, bicycles are human scale devices conceived around the idea of human power. Maybe there's a role for a small motor to help someone do what they no longer can on their own, or accompany their more athletic significant other or younger relative, or arrive at work (albeit only on a nice day) less than sweaty - get some of the outdoor experience and parking simplicity, but none of the fitness reward.

Meanwhile motor vehicles come in a variety of shapes, sizes, and wheel counts with a variety of efficiency, convenience, and safety rates to match. The motorcycle is hardly a new idea.

There are all sort of answers, but let's not pretend one thing is something else.