To add more background to the reason the SFCTA may be considering regulation, reader Yoyo did some digging and left this comment regarding the legal issues of shuttle buses:
California V.C. section 35400(10)(A) states that buses up to 45 feet (that's the length of the Setras) can have reasonable access between highways and "points of loading and unloading for motor carriers of passengers". So the size itself isn't in violation, and these buses do travel to Noe Valley and other neighborhoods to load and unload passengers. The question remains: what is reasonable access?[NVSF: Shuttle Buses: Useful or Menace?]
Here, the SF transportation code has something to say. Section 501 lists a whole host of streets on which heavy vehicles (over 6000 lbs.) are forbidden; a number of these are in Noe Valley west of Church, but Sanchez is not included. Section 7.2.87 also forbids commercial passenger vehicles (capacity 8 or more) from the streets listed in Section 501 (the code says 503, which doesn't exist; 501 appears to be the correct referenced section, from an old version of the code).