The aerodynamic advantage of recumbents became obvious in the 1930s when a middle-ranking rider beat all the top professionals - so the cycle racing establishment promptly banned them. The UCI remains in a state of denial to this very day, so if you want to know how fast a human being can actually go on a bike, you should enquire elsewhere.
CTC, fortunately, is not bound by the pernickety rules of cycle racing. We welcome any kind of cyclist on any kind of cycle, recumbents certainly included.
Wind resistance, however, becomes relatively less important when cycling for transport rather than sporting purposes. Other factors may literally outweigh the aerodynamic advantage in hilly areas and a lower centre of gravity, surprisingly, makes balance more tricky. So tricycle recumbents are more accessible, but even heavier, more bulky and inconvenient to park and store. And because the force of pedalling is resisted by the back of the seat rather than gravity, recumbent cyclists must make a hard choice between comfort and efficiency.
So it is that recumbents often fail to deliver more speed for less effort - except in flat country - and of the few people who use them for everyday transport, many do so for other reasons. These reasons are often in avoidance of physical problems brought on by attempts to make the standard cycling position more aerodynamic, where leaning forwards may throw excessive weight onto the hands and wrists, bend the back and hyperextend the neck. A recumbent cures all these problems by relieving the arms of any weight, supporting the back and flexing the neck the opposite, healthier way.