Average speeds are fun to discuss but I wouldn't take them too seriously. The biggest factor which brings down average speed is the time spent averaging in zeros or very small numbers.

In the days before cycle computers, "average" speed was calculated exactly as its name implies - total distance divide by total elapsed time from start to finish. (Remember your physics classes?

) Nowadays computers stop counting when you aren't moving, so your down time doesn't get included. It makes you feel better because the numbers look better. But even so they still count time spent walking the bike, slowing for intersections, etc. Spend much time doing that and your computed fake-average speed can fall significantly.