My 8.7 mile inbound commute usually takes about 50 minutes by the clock. My computer, which measures only actual moving time registers anywhere from 38-44 minutes, depending on wind and just how I feel. On flat land with no wind, I usually maintain 15-16 mph by the speedometer, but with decelerations and accelerations at stop signs and red lights the average drops to 13-13.5. For all of the reasons mentioned, you have to allow for slower speeds and elapsed times commuting than you can achieve on more open roads.
Regards,
Raymond