At 2 p.m. today, 500 protesters will participate in the “John T. Williams Memorial March and Rally.”  The march will start at Boren Avenue and Howell Street; head north on Boren to Virginia Street;  then west on Virginia; stop at the Seattle Police Department West Precinct on Virginia at Eighth Avenue; continue west on Virginia to Fifth Avenue; turn left at Fifth and move south on Fifth to City Hall.  The march and rally is expected to end by 4:30 p.m.; however, it will likely impact traffic throughout downtown and in particular, the afternoon commute.