League of American Bicyclists, chalk 50% of all crashes up to operator error. We are perfectly capable of bringing ourselves to the ground all on our lonesome. The final 33% of crashes cover everything else: Bicyclists hitting (or being hit by) animals, other bicyclists, or something other than a car.
It's this last category that interests me, since during Bike to Work Month, the number of bicyclists on the road -- and thus the likelihood of colliding with another bicyclist -- increased dramatically. This means that lots of people who normally only ride on weekends hop in the saddle during normal commuting hours and start working on logging those miles.
What did this wonderful increase in cycling mean for me personally? More than anything else, I experienced a dramatic increase in stealth passing, usually by bike path racers. Innumerable times on my commute, I would be blithely pedaling along and suddenly find another cyclist next to me, often much closer than was safe, ghosting by with nary a word or ding-a-ling. Not only did this discourtesy irritate me, it endangered me unnecessarily.
I love to see more people bicycling, and I dream one day of living in a society where nobody bats an eye at biking for transportation because it's as normal as driving is right now. But I hope that when that day comes -- and you can be sure it will come -- it comes with a good dollop of on-bike courtesy, too. Let's start making that dream a reality: take a moment to politely call "On your left" or ding a bell next time you pass somebody.