The AlertDC system, responding about four hours late to the game, is reporting that the water main break at 16th and L Streets NW that throttled downtown traffic this morning is not estimated to be repaired until 6 p.m. at the earliest. That means you should plan on your trek home possibly being as infuriating as the trip to the office was this a.m. DDOT is still advising motorists to avoid 16th and 17th Streets downtown.