This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
Recumbents hold all of the human-powered speed records. This is
because they are aerodynamically superior to conventional bicycles;
less frontal area means less wind resistance. The Lightning F-40
currently holds the Race Across America speed record of five days and
one hour. Gardner Martin's Easy Racer Gold Rush, ridden by Fast Freddie
Markham, was the winner of the Dupont Prize for breaking 65mph. You
can currently buy production versions of these bicycles. Fairings for
street use are common and optional equipment on most commercially built
models. They protect you from rain, cold and wind, with up to a 30%
reduction in drag. Commercially available recumbents are not always
faster than conventional bicycles. It depends mainly on the individual
rider. Your best bet is to do you homework and if your goal is
performance and speed, be sure that you look for a recumbent designed
for this purpose.