I have been looking at the wait times on the Dulles web site:
http://www.flydulles.com/iad/security-information
I shows security wait times like 5 minutes for the East Checkpoint and 1 minute for the West Checkpoint. At 4:00 PM on a weekday.
Is this site accurate?
I rarely use IAD but from personal experience at other major US airports, security wait times are never that short on a weekday afternoon at 4:00 PM