Taking the metro is a bit faster than cycling, I consider myself to be an okay shape. I still need to lose about 20 lb to get to where I want to be, and I still don't think I'd be up to the challenge of hopping on a bike for all my commuting needs.
If you want to propose something, you have to factor in what people are willing to actually do. The typical overweight American, it's not going to be open to biking 4 hours a day to get to and from work.