Instead of "bragging" in a separate thread, I thought I'd post this here. Just made my commute at an 18.1 mph average. But that's just over 6 miles. First time for me on a commute, though. I got to the edge of campus, reset my computer and suddenly got a fire lit up under me for no reason. I still had to go slower than I wanted to at points. There were a couple of school zones in a section that I could have easily done 23 or more mph, so cars slowed me down (imagine that...) and I hit 3 freakin' lights on the last really long leg. I saw my average go down from 18.7 to 18.1 at one stop light because I was trying not to come to a complete stop. I'm usually a little tired in the morning and riding home in the dark at night, so on good days, I'm usually closer to 16 mph at a more comfortable pace. I would like to see if I could hit the magic 20 mph mark. Maybe if I time the lights right one day or something.

I'd say if you had a nice, open route with few lights and little traffic and a set of aero bars, a reasonably healthy person could pull 20 mph averages, but maybe not every day.