Your quality of life would presumably improve due to cleaner air and less pollution. If you take public transit you are also lowering your carbon footprint and alleviating congestion, improving quality of life for you and everyone else in town. If you walk or bike (I bike every day and find it faster to get to work than driving in rush hour traffic, in fact), you are getting a little cardio out of the deal and improving your quality of life. And presumably if enough people opt to walk/bike/transit, investment in that infrastructure will follow and quality of life in that department will also improve.

The true costs of our luxury goods like a personal car are completely hidden to us. It's important to realize how harmful to quality of life certain luxuries we are accustom to really are.