Let's see, I did my fastest commute yesterday, in fact: Road bike (vintage), 800/600 feet of climbing/descending; 3 miles on a MUP, 5 more miles on LA streets. I averaged just over 14 mph, including stops and everything. Rather happy with myself that I was under 40 minutes for the first time.
Over time this year, including a few rides that were not commutes, I seem to be averaging about 12 mph. Vintage road and MTB (what they call a 'hybrid' these days).
Maybe I'll set my tracker to stop recording when I stop. Might get me an extra half-mph or so, right?!