Is that little dirt road detour in Vienna still there? Might be one thing to consider if you'll be riding on skinny tires.

Also, keep in mind that it's ALL uphill coming back to Herndon. I rode all the way to Shirlington and bonked halfway back to Herndon on my first round trip last year. (Of course, when you tell your grandkids about how you bike commuted when you were their age, it will be Uphill Both Ways.)