I track my time and average speed on all of my commutes, and my personal best is 17.25 mph over 22 miles round trip. I doubt if I could improve much on that on my commutes due to red lights, traffic, wind. Red lights will destroy your average speeds, even if your computer is set to stop timing during stops. A stiff head or cross wind will do the same. My route is very hilly, so my legs have to be well rested to post good times, and my typical average speed commuting is about 15 mph.
I enjoy tracking my times and shooting for personal bests. However, don't risk your safety by trying to set new speed records. Running red lights and blowing stop signs are sure ways to get run over or cause an accident. However, charging the hills and improving your climbing times will really help your average speed.