It seems that when persuading people to go car free or car lite, the gist seems to be around saving money, the environment, etc... which is definitely not always true, and seems to be ignoring the best, most convincing argument for biking that is almost always true. Health, health, and your health! In the states, the three largest killers (Fig.3 ) seem to be heart disease, strokes, and cancer. Guess what increased biking does to these risks? In 1986, the British Journal of Industrial Medicine
I'd bet that having the average fitness level of those who are a decade younger than you puts you in their risk group for heart disease, strokes, and certain types of cancers. Significantly reducing your chances of dying. Bicycling compared to driving may also reduce fossil fuel consumption slightly, and may save you a bit of money, but that really depends on context. For example, most people aren't in shape, so getting in shape will most likely result in a healthy/less fossil fuel intensive diet and reduce some or all of your gasoline use. Otoh, if an individual is already healthy, then biking everywhere may use as much in terms of fossil fuels as driving an efficient car the same distance due to lack of reduction in diet, and the current fossil fuel overhead. Not to mention it may not be practical for larger distances. For some people, giving up their car may require them to use public transit which can more more expensive, and less convienient. It's a YMMV deal....studied 1,394 people and found that those who cycled regularly had the fitness levels of people ten years younger. The second paper was published in the Archives of Internal Medicine in 2000. It was a fifteen-year study of 13,375 people and found that those who cycled to work were much less likely to die prematurely than those who did not. The report concludes, "Even after adjustment for other risk factors, including leisure time physical activity, those who did not cycle to work experienced a 39% higher mortality rate than those who did."
So, bicycle because you'll live longer, and probably be happier, not because of any other reasons. If I want to cut my fossil fuel use, then it's much more effective to cut my electricity usage or get a more efficient car and modify/drive it for efficiency, than bike places. Getting a driving a geo metro slowly should allow for ~100mpg depending, and building your own EV along the lines of vw's 1L car would be the hands down winner of a bicycle in terms of fossil fuel use. If you reduce your electrical consumption enough you may be able to run everything off of solar or win electricity. Build your own house with lots of insulation and evaporative cooling. I've heard it can be done such that it's in the high 70's inside when it's in the 110's outside on a few hundred watts and effective design. Never buy new, DIY, and don't mix your issues!