Imagine giving millions of American families tax free rebates of thousands of dollars a year ($5k to $10k would be common) and making a big dent on obesity. It has been demonstrated in other parts of the world, but it may be politically impossible in America.
We've mentioned John Pucher of Rutgers. He has done public policy studies on human powered transportation for some time and has carefully sorted out why biking works in Northern Europe and not in the US. Recently he put together a three part summary in Momentum Magazine
part one focuses on safety
part two on parking
part three on training (cyclists and drivers) and restricting cars
He argues that a systematic approach is needed to make biking a mainstream activity. The countries where biking is practical spent decades getting there. It is possible in the US and some cities are going in that direction, but baring dramatic external forces (say $10 gallon gasoline), it seems unlikely that widespread bike use in coming anytime soon.
snip
Cycling remains a marginal mode of transport in most North American cities because it is widely viewed as requiring special equipment and training, physical fitness, and the courage and willingness to battle with motor vehicles on streets without separate bike lanes or paths. Cycling is a mainstream mode of urban travel in Northern Europe precisely because it does not require any of those things.
Providing safe and convenient rights of way is the most important element in making cycling possible for everyone, but it alone is not sufficient. The remaining two articles in this series examine other, complementary and necessary policies.
There are clearly health and family-level economic benefits if you can bike safely and can shed a car. A few towns and cities are moving in that direction, but try to present some of these ideas to your local city council.
A video of one of John's talks is
here.

Perhaps a marketing approach is necessary. In the early sixties motorcycles were considered unrespectable. Something big, noisy and ridden by someone you wouldn't want your kids to know.
Honda had a brilliant ad campaign to introduce a very small 50cc motorcycle - "You Meet the Nicest People on a Honda"
Bikes seen to be used for recreation rather than utility in the US. Bicycle companies sponsor racing, but this only addresses a small segment of the population. I haven't seen the message that regular people can use bikes for some of their trips.
Making a real dent in a land where the car is so entrenched is tough sledding and I would imagine any policies that severely discourage cars are non-starters. If biking can be made safer through bike paths and better intersections, perhaps a larger segment of the population would use them. It may be possible to have a larger positive impact than high speed rail would give for a fraction of the cost and with the added benefit of a healthier population.