And how much risk you want the people around you to assume on your behalf. I sometimes commute (40mi) home from work, mostly on an off-road rails to trails paved bike trail. One of the few complaints I have about this trek is the people who are completely oblivious when I say "on your left" and ring my bell. I wind up having to stay behind them, yell, or just go around them, which sometimes startles them. It's imperative that you're present enough to both send and receive communications from people around you.