I've been commuting by bike for over a year now. On a perfect day where there is light traffic and few red lights (about 10% of the time) I can shave off 10 minutes driving vs bike. However, more often than not, there is heavy traffic, accidents, etc and it's about the same time wise. What I really love though are Friday afternoons, where traffic is insane, accident, traffic backed up 2 miles and I zip through onto my bike trail whistling without a care in the world. I will never give up the bike!