I've always assumed it was a matter of risk assessment, that women who feel less safe are more inclined to drive rather than expose themselves in the open. Natalie Ramsland, the bike builder at Sweetpea Bicycles in Portland told me something this morning that really gave me food for thought.
I suspect that the broader scope of women's responsibilities (work, caregiving, schelppin') plays some role female ridership. It's easier to be the heroic bike commuter if you've got somebody else picking up the drycleaning and shuttling Johnny off to soccer practice. It seems that too often that somebody is female.This is certainly true in my family; while I'm busy self-righteously saving the planet, my wife is busy running errands and taking care of the household.
It's time for me to be a little more appreciative of my wife and to evaluate how I can contribute more to the household, I think.
You can read more about Natalie in this interview at Commute By Bike.