Washington Metro systems shuts down for over a day in the middle of the work week. Officials cite "safety concerns." There was a terrorist alert issued the day before for DC area hotels and convention venues.
https://www.washingtonpost.com/local/trafficandcommuting/washington-braces-for-full-day-of-metro-shutdown-to-deal-with-safety-concerns/2016/03/16/42324598-eb3f-11e5-b0fd-073d5930a7b7_story.html

http://www.bizpacreview.com/2016/03/14/dhs-warns-of-possible-washington-d-c-terror-attack-hotels-convention-centers-on-edge-316829