Hah…I thought you would bite at that one 
For us normal mortals I think 12 ~ 15mph is the average on a flat road over any type of distance. And I have to say a lot bicyclists do not do themselves any favors with the way they ride, and I am come from a family of bicyclists so if they annoy me then god only knows how much they annoy others. But this is getting way off topic here
