While it is VERY questionable that Loud Pipes save lives. I personally believe that a certain amount does help, (and I don't see a high accident rate for Prius's) but then I have ridden both quiet and loud and found that either way ultimately it is only I that can SAVE me. The 1st thing I learned in CHP moto school was YOU ARE INVISIBLE! no one will see you ride as such.
To leave a noise question to the "judgment" of an officer is highly a questionable choice! If in fact they want to have a law if any this should be subject to some measurement. Let's say 80dB or 100dB at 20 ft. This means the BOOM stereos too. BUT Seems to me they can't even keep people OFF cell phones.
"Quieter streets". (what a quint concept) Might as well make downtown a pedestrian zone only.
Electric transit buses, etc... Why not?