This gets to a huge problem in vehicle classification. An older man in my family is blind on one eye and can't see too well out of the other, and lives alone in a rural part of the country that gets snowy in the winter. He can drive, but only a scooter; a scooter cannot have more than three wheels. There was a few years when he was allowed to drive a four-wheel enclosed scooter that kept him safe and warm in the winter, but the rules were changed again and now he's back to needing help half the year.
It seems like such a stupid thing, but the huge distinction that is made between three and four wheels causes all kinds of problems. Now that electric bicycles have come to stay it's high time it's rethought.