> 4) Are typically more compact than a black cab - take up less road space

I thought "that can't be right, black cabs aren't all that big". And a quick search suggests that a Prius and a TX4 black cab are pretty much the same length - 454cm (Prius) vs 458cm (cab).

The black cab is 18cm wider, which may make a difference, although length seems the more significant dimension here. And black cabs are much taller of course.