I can see Knucklesandwich's point about crossing Lee Highway near the 66 off ramp in the evening since a lot of people live around there and would be exiting 66 at this point. However, in my experience both driving and biking in this area, in the morning fewer people get off 66 at the off ramp at this location. Instead, most are blowing by trying to get to DC. So, while you always have to be alert for cars, I would expect them not to be as much of a problem in the morning as compared with the evening.

On a related note, I sent an email to the Arlington County bike people--at least the ones I discovered on line. I alerted them to this problem and explained that at the very least a sign would be helpful, perhaps even some weekly leaf blowing/sweeping in the fall. I'll keep you all posted about what happens.