I wish my reasons were more altruistic. I've been an avid cyclist all my adult life. I simply started bike commuting to get to ride more.
I think that John Forrester (Effective Cycling) is right that many folks that bike commute (at least in the US) do so because they enjoy cycling and it lets them cycle more. While I do think that times are changing, and issues like traffic congestion, parking, health, financial and fitness are bring more folks to consider bike commuting, I still believe that most in the US do so simply because they are bike adicts.
Dave,
who is a **** for big miles, and worships at the house of the big chainring.