Highly depends on the time I leave the house. My commute is 15 miles and consists of a few miles of neighborhoods, about 1-2 miles of arterial, and then close to 10 miles of 2-lane rural.

The only time I've actually bothered to count was when I left the house at around 5:00 AM to make a 7 AM morning meeting, and in those cases I often will only have 5 or 6 cars pass me in 15 miles, and most of those are closer to work when it's past 6 AM at that point. When I leave the house between 6 and 6:30 there's much more traffic, and then even more at 5 PM. I would estimate the count to be 100 cars or more.