My daily commute is one mile. (You're jealous, aren't you.) But it was two degrees today (that's Fahrenheit) and dark. The powder wasn't too deep, though--that's good. On freshly plowed roads, I can do about 8-10mph in winter. On snow-covered roads, that speed can easily be cut in half. The primary limiting factor in those conditions is how long you are willing to stay out in the cold. Secondarily, the limiter is how bad the roads are. Distance isn't all that important, but I usually stay within about five miles this time of year.

I have, though, devised a brilliant and scientifically provable formula by which to determine whether a commute qualifies as "long." This is it:

(Bt > (1.5Dt or (Dt + 20m))) = LC

Bt is the amount of time it takes to traverse the commute distance by bicycle, and includes the time it takes to lock up the bike and any additional time that is necessary for changing clothes and the like. Dt is the amount of time required to traverse the commute distance by car, and includes the time required to park and walk from there. m is minutes. LC is a long commute. Therefore, if bicycling takes more than 150% of the time that would be required to drive, then it is a long commute. And if bicycling takes more than 20 additional minutes over the driving commute, then it is a long commute.

The formula does not account for the cost of parking, relative danger, or "cool factor." Otherwise, it is empirically proven and immune to challenge.