A safe rider would not spend any time next to a cage, and would know before overtaking the cage if the driver was using a cell phone, would take steps to better the odds that the driver saw him, etc. If that doesn't work there's a little button on the left side of the handlebars that makes noise when you press it. Imagine if every bike on the road sounded an air horn every few seconds no matter where they were. Pretty annoying, don't you think? That's how the general voting public views loud pipes. And that's why we're seeing more attempts at legislating our freedoms away. It's only a matter of time before some laws begin sticking and municipalities start relying on enforcement as a cash cow.