I'm glad the park service is being somewhat scientific about this, rather than just banning bikes from national parks. I love bikes, I love the sound of a good running engine, and I appreciate a sweet exhaust note, but I think some folks get carried away. Here in downtown DC, it's not unusual to hear noisy cruisers purposefully blip the throttle hard when running between buildings - just so they can hear the echo. If you've spent any time on Skyline Drive, they do the same thing in the tunnel. I am a live and let live guy, but I'm far less willing to "let live" when a small group of thoughtless people being intentionally obnoxious could potentially limit my opportunity to enjoy my motorcycle in some of America's most beautiful places. Motorcyclists in general get stereo-typed enough as it is because of the actions of a few boneheads (thinking also of the stunt-riding sport bike guys popping wheelies in traffic at 90+ MPH).
Chris