I know there are many of us in the neighborhood who use Powell Blvd to get downtown, and to I5. The weekend of July 20-22, 2012, SE Powell Boulevard will be closed for several blocks on either side of the SE 17th Avenue/Powell Boulevard overpass, with crews working 24 hours a day to demolish the overpass structure in preparation of the construction of the MAX Orange Line. The work is being performed around the clock in order to minimize the closure period.
Holgate Blvd will be the detour route during the time Powell Blvd is closed. A PDF map of the detour can be found here.
Click for more detailed information from Trimet.