Shuttles run about every 5 minutes during much of the day.
Today it was more like 20 minutes for the GOLD buses to show up (this was around 4 pm).

The shuttles are totally mis-managed at Dulles for their remote lots, with the wrong # and type in each of the lots. The drivers are not allowed to bypass a stop, even if a bus is already stopped there. Today, after waiting those 20 minutes, 2 GOLD buses showed up
together!
Originally Posted by scubadiver
Non-locals to Reston/Herndon may consider using municipal parking at Reston Town center, and taxi or hotel shuttle to IAD.
I hadn't considered this option, I might try that the next time I take a weekend trip.