I figure I save about $400 per month, offset by about $50 in bus fares. So about $350 monthly. My wife and I own one car which is mostly hers. I either commute by bike or ride the bus, depending. When we sold the second car 10 years ago, I rationalized that if I needed a car occasionally, I could rent from the Enterprise 2 blocks away. In ten years I have done that twice. Reducing or going totally car free depends on where and how you live. I live in an older neighborhood that has all the 'stuff of life' in walking distance. My kids are grown. My needs are few. It is very easy for us. Perhaps as age encroaches, my choices may change.
When we were raising kids, we lived suburban. 2 cars were necessary, we felt, though we were certainly conflicted. Where safety is the dealbreaker as to cycling in the city, the same applies to navigating suburbia.