My commute, through downtown Atlanta, averaging 20mph just not possible. I don’t really think I could do it driving either since it takes about the same time for me to drive my 9 miles as it does to bike it.

Maybe other people can do it in other parts of the world. For me though, my comfortable cruising speed is about 15mph, which makes the commute average out to about 12mph including hills and stops. Yeah, I have a 30lb Surly with panniers, so it’s not exactly fast. But I just can’t really imagine averaging 5mph faster. There are lots of folks in little road bikes that pass me everyday, but they are never that much faster and I can generally keep up if I push it.

I doubt people who who quote high average speeds, but I could be wrong. But why do that on a commute? I want to be reasonably comfortable. Averaging 20mph on a road bike that can maintain that, can’t possibly be comfortable for very long.