Averaging 20+ MPH on any ride is a challenge, and not likely on a urban route (unless you have greenway routes that keep you away from lights and traffic).

This is my old commuting route with my fastest ride home (I don't work or live at these locations any more, so no risk sharing). It is a rolling route, but I had a good tail wind and on a road bike, plus it's a suburban route with only 4 or 5 of stop lights.