We missed the formal announcement toward the end of last week that Metro’s board has approved the new S9 Metrobus line, the long-discussed 16th Street rush hour express bus. Metro says it plans to begin S9 service as early as the end of March. Instead of the more than 80 stops on the S1, S2 and S4 routes between Silver Spring and Federal Triangle or Potomac Park, the S9 will serve only 16 stops…