I have an 11 mile commute. 4 miles is gravel road, sometimes somewhat washboarded, but not terrible. The rest is paved. There are a dozen or so short hills, perhaps 40 feet of rise/drop on each. SE Michigan glacial holes, for those familiar.

In warm weather my average is about 16.5 MPH. I have made nearly 18 on really good days.

I just checked my comp, and this morning my avg was 13.9 MPH, at 13*F, the gravel road section was only mildly rutted. The worst I have done is last week after heavy snows, there was some rutting that nearly dumped me several times and really slowed me down, and the temp was -3*F; my avg then was 13.6 MPH.