I don't think Falls Church to Herndon would be too bad during morning rush hour, but I am not sure how bad the westbound toll plaza on the Toll Road is in the morning. Evening commute would be ok until you get close to 66. And again, a lot can change based on exactly what time you'll be commuting, to exactly where. "Herndon" has a somewhat wide definition. You can be in Herndon working right off the Toll Road or be 2 exits down Rt. 28 in one of the EDS buildings.

My wife had a co-worker who commuted Falls Church to Herndon; I'll have her ask how long it took her.