This points out the mental adjustment between riding for training/recreation and commuting. I recently started commuting once a week, fixed gear, 21 fairly hilly miles each way. Instead of trying to keep my pace up, pushing it, and going 16 mph, my goal was getting to work comfortably. So I average, with lights & intersections, 14 mph. Overall, the difference is 10 minutes, but then I work 8 hours and have to turn around and do it again. Different priorities. It's very satisfying to use the bike for something more practical (and gas saving) than a weekend loop.