Ryan,
You forgot to factor in the single tracking, derailments, fires, trains being pulled out of service, weekend track work, etc., etc. :giggle:
EDIT: Oh, I forgot about the new speed restrictions that very recently went into effect - like 15 mph between L'Enfant and Pentagon in both directions (according to Metro's trip planner it will now take 17 minutes between the two stations) for at least the next 6 to 8 weeks - that will add some 'quality time' to your sojourn on Metro! :help:
EDIT, EDIT: The above speed restriction is not posted at WMATA's website today, so it might be only on weekends, or the situation has been resolved, or Metro is being flakey, or etc., etc.