I had to vote 13. That gives me the committed 13 miles and the option to extend it. My current commute is 7 each way and it just isn't enough.
Incidentally if I was voting in the summer I'd vote 18, and again with the option to extend it. I'll take 100°+ days any time over the chill of winter (anything less than 40°F is chill of winter to me...).