Over the almost five years I have been tracking my commute data, my year round average has consistently stayed in the 14 mph range, and is slower in the winter. I mostly ride a 30+ pound hybrid between 25 and 30 miles round trip on a combination of MUPs. My slowest commute was about at a 7 mph average riding in about four inches of wet snow on uncleared MUPs, my fastest was about 17 mph on one of the few times I commuted on my road bike.