Since it happens to be closed off to traffic from Mariposa to 19th. Something is going down near the 18th Street intersection, as there are firetrucks, cruisers, and even DPT Cushmans on the scene, in addition to that auspicious black truck-van. So, unless you prefer to be late in whatever endeavors you undertake this morning, try to find another route.
UPDATE!!! Apparently this closure was due to the fact that GRENADES were found there! Too much Call of Duty, folks.
Apparently they found grenades in a house there!
http://www.sfgate.com/cgi-bin/article.cgi?f=/baycitynews/a/2011/02/03/grenades03.DTL
http://www.ktvu.com/news/26729031/detail.html