I hear the "it'll mess up my hair/I can't wear nice clothes" excuse a lot. But I think there's more to than than simple vanity--women are much more likely to be criticized in a corporate workplace for inappropriate dress, or judged based on their appearance rather than their competence, than their male counterparts are.

There's something to that too, I think. But I also think there's a misconception about what kind of risks there are--on a bicycle, you might get in an accident, you might have a mechanical problem, etc, but those are things that you have some amount of control over if you are skilled at riding and have the willingness to learn some basic repairs. And yet many women I've talked to are unreasonably afraid of the least common forms of attack--namely, being assaulted somehow. You are much, much more likely to be assaulted by someone you know, in a place where you think you're safe, than you are to be jumped on your bicycle--and yet a lot of people I've talked to seem to think it's a major danger.